As filed with the Securities and Exchange Commission on October 18, 2006

Registration No. 333-136039

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

Amendment No. 4

to

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

CATALYST PHARMACEUTICAL PARTNERS, INC.

(Exact name of registrant as specified in its charter)

220 Miracle Mile

Suite 234

Coral Gables, Florida 33134

(305) 529-2522

(Name, address, including zip code, and telephone number,

including area code, of registrant’s principal executive offices)

Patrick J. McEnany

Chief Executive Officer

Catalyst Pharmaceutical Partners, Inc.

220 Miracle Mile

Suite 234

Coral Gables, Florida 33134

(305) 529-2522

(Name, address, including zip code, and telephone number, including area code,

of agent for service)

Copies To:

     Approximate date of commencement of proposed sale to public: As soon as practicable after this registration becomes effective

     If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act, check the following box:    o

     If this Form is used to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration number of the earlier effective registration statement for the same offering:    o                            

     If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering:    o                            

     If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration number of the earlier effective registration statement for the same offering:    o                            

     The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to Section 8(a), may determine.

EXPLANATORY NOTE

      This Amendment No. 4 to the Form S-1 is being filed solely to file Exhibit 5.1.

PART II

Information Not Required In Prospectus

Item 13.     Other Expenses of Issuance and Distribution

          The following table sets forth the various costs and expenses to be incurred in connection with the issuance and distribution of the securities registered under this Registration Statement, other than underwriting discounts and commissions. All such expenses are estimates, except for the SEC registration fee, the NASD filing fee, and the Nasdaq Global Market listing fee. The following expenses will be borne solely by the Registrant.

Item 14.     Indemnification of Officers and Directors

          Section 145 of the Delaware General Corporation Law permits, in general, a Delaware corporation to indemnify any person who was or is a party to any proceeding (other than an action by, or in the right of, the corporation) by reason of the fact that he or she is or was a director or officer of the corporation, or served another business enterprise in any capacity at the request of the corporation, against liability incurred in connection with such proceeding, including the estimated expenses of litigating the proceeding to conclusion and the expenses actually and reasonably incurred in connection with the defense or settlement of such proceeding, if such person acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, the best interests of the corporation and, in criminal actions or proceedings, additionally had no reasonable cause to believe that his or her conduct was unlawful. A Delaware corporation’s power to indemnify applies to actions brought by or in the right of the corporation as well, but only to the extent of expenses (including attorneys’ fees) actually and reasonably incurred by the person in connection with the defense or settlement of the action or suit, provided that no indemnification shall be provided in such actions in the event of any adjudication of negligence or misconduct in the performance of such person’s duties to the corporation, unless a court believes that in light of all the circumstances indemnification should apply. Section 145 of the Delaware General Corporation Law also permits, in general, a Delaware corporation to purchase and maintain insurance on behalf of any person who is or was a director or officer of the corporation, or served another entity in any capacity at the request of the corporation, against liability incurred by such person in such capacity, whether or not the corporation would have the power to indemnify such person against such liability.

          The Registrant’s By-Laws implement the indemnification provisions permitted by Section 145 of the Delaware General Corporation Law by providing that:

          In addition, as permitted by Section 102 of the Delaware General Corporation Law, the Registrant’s Certificate of Incorporation includes a provision that eliminates the personal liability of its directors for monetary damages for breach of their fiduciary duty as directors to the fullest extent permitted by the Delaware General Corporation Law.

          These indemnification provisions may be sufficiently broad to permit indemnification of the Registrant’s directors and officers for liabilities (including reimbursement of expenses incurred) arising under the Securities Act. Pursuant to the Underwriting Agreement to be filed as Exhibit 1.1 to this Registration Statement, the underwriters have agreed to indemnify the Registrant’s directors, officers, and controlling persons, and the Registrant has agreed to indemnify the underwriters, against certain civil liabilities that may be incurred in connection with the offering of securities pursuant to this Registration Statement (including certain liabilities under the Securities Act) as a result of any statement or omission in this Registration Statement, in the related prospectus, in any preliminary prospectus, or in any amendment or supplement thereto, in each case to the extent that the statement or omission was made in reliance upon and in conformity with written information furnished by the underwriters expressly for use therein.

Item 15.     Recent Sales of Unregistered Securities

          The following is information furnished with regard to all securities sold by the Registrant within the past three years that were not registered under the Act.

          On February 28, 2005, the Registrant completed a rights offering of shares of its authorized but unissued common stock to holders of its common stock and holders of its Series A Preferred Stock. In the rights offering, the Registrant issued 3,954,483 shares of its common stock to its stockholders. No commissions were paid in connection with the issuance of the foregoing shares, all of which were issued pursuant to an exemption from registration under Section 4(2) of the Act. This offering resulted in proceeds of approximately $1,000,000 to the Registrant, net of expenses.

          On July 24, 2006, the Registrant completed the sale of 7,644 shares of its Series B Preferred Stock, par value $0.01 per share at a price of $435 per share. The foregoing securities were issued to 51 accredited investors and were issued pursuant to an exemption from registration under Section 4(2) of the Act.

          In July 2006, the Registrant issued an aggregate of 142,274 shares of its common stock to five of its advisors for services performed during 2005 and through June 30, 2006. These shares were issued pursuant to an exemption from registration under Section 4(2) of the Act.

          None of these transactions involved any underwriters, underwriting discounts, or any public offering. The recipients of securities in each transaction represented their intention to acquire the securities for investment only and not with a view to or for sale in connection with any distribution thereof, and appropriate legends were affixed to the stock certificates and instruments issued in such transactions. All recipients received adequate information regarding the Registrant and the stock sold.

Item 16.     Exhibits and Financial Statement Schedules

(a) Exhibits

(1) Previously filed.

 *  Filed herewith.

(b) Financial Statement Schedules

          None.

Item 17.     Undertakings

          (1) The undersigned registrant hereby undertakes to provide to the underwriters at the closing specified in the Underwriting Agreement certificates in such denominations and registered in such names as required by the underwriters to permit prompt delivery to each purchaser

          (2) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers, and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer, or a controlling person of the registrant in the successful defense of any action, suit, or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

          (3) The undersigned registrant hereby undertakes that:

SIGNATURES

          Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant has duly caused this Amendment No. 4 to Registration Statement on Form S-1 to be signed on its behalf by the undersigned, thereunto duly authorized, in City of Miami, State of Florida on October 18, 2006.

          Pursuant to the requirements of the Securities Act of 1933, this Amendment No. 4 to Registration Statement on Form S-1 has been signed by the following persons, in the capacities and on the dates indicated.