UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): April 23, 2012

Nabi Biopharmaceuticals

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (301) 770-3099

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On April 23, 2012, Nabi Biopharmaceuticals (“Nabi”) issued a press release announcing the execution of a merger implementation agreement, dated April 22, 2012, between Nabi and Biota Holdings Limited (“Biota”), an Australian company, pursuant to which, among other things, Nabi and Biota will form a combined company to be named Biota Pharmaceuticals, Inc. The combined company is expected to be listed on the NASDAQ Stock Market and headquartered in the USA. A copy of the press release is filed as Exhibit 99.1 to this report and incorporated herein by reference.

Additional Information

This report is being filed in respect of the proposed merger and related matters involving Nabi and Biota. In connection with the proposed transactions, Nabi will file with the Securities and Exchange Commission (“SEC”) a proxy statement and will mail or otherwise disseminate the proxy statement and a form of proxy to its shareholders when it becomes available. SHAREHOLDERS AND INVESTORS ARE ENCOURAGED TO READ THE PROXY STATEMENT (AND OTHER RELEVANT MATERIALS) REGARDING THE PROPOSED TRANSACTIONS CAREFULLY AND IN ITS ENTIRETY WHEN IT BECOMES AVAILABLE, AND BEFORE MAKING ANY VOTING DECISION, AS IT WILL CONTAIN IMPORTANT INFORMATION ABOUT THE TRANSACTIONS. Shareholders and investors will be able to obtain a free copy of the proxy statement (when available), as well as other filings made by Nabi regarding Nabi Biopharmaceuticals, Biota Holdings Limited and the proposed transactions, without charge, at the SEC website at www.sec.gov. In addition, documents filed with the SEC by Nabi will be available free of charge on the investor relations portion of the Nabi website at www.nabi.com.

Certain Information Regarding Participants

Nabi and certain of its directors and executive officers, may be deemed, under SEC rules, to be participants in the solicitation of proxies from its shareholders in connection with the proposed transactions. The names of Nabi’s directors and executive officers and a description of their interests in Nabi are set forth in Nabi’s Annual Report on Form 10-K for the fiscal year ended December 31, 2011, which was filed with the SEC on March 14, 2012, and Nabi’s Proxy Statement dated April 20, 2011 which was filed with the SEC on the same date. Additional information about the interests of potential participants will be contained in the proxy statement (when filed) and other relevant materials to be filed with the SEC in connection with the proposed transactions. These documents may be obtained from the SEC website and from Nabi in the manner noted above.

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The following document is filed herewith as an exhibit to this report:

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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EXHIBIT INDEX