SONUS Pharmaceuticals Announces Dismissal of MBI and Mallinckrodt Lawsuit To Invalidate SONUS Patents

         SONUS Files Patent Infringement Lawsuit Against MBI in Seattle 

BOTHELL, Wash., Jan. 7 /PRNewswire/ -- SONUS Pharmaceuticals, Inc. (Nasdaq: SNUS) today announced the dismissal of a lawsuit filed by Molecular Biosystems, Inc. (MBI) and Mallinckrodt, Inc. in the United States District Court for the District of Columbia, seeking declarations that certain SONUS ultrasound contrast agent patents are invalid and unenforceable and that SONUS had made false public statements and engaged in other actions intended to damage MBI and Optison(TM).

SONUS also announced today that it has filed a patent infringement lawsuit in U.S. District Court in Seattle against MBI and Mallinckrodt, alleging MBI's Optison(TM) ultrasound contrast agent infringes one or more of SONUS' patents. SONUS has eight U.S. patents that include 170 claims directed to compositions of matter and methods of use of various fluorocarbon-based ultrasound contrast agents.

"We are pleased that the Court has dismissed this lawsuit in the District of Columbia and that we can now proceed forward with enforcement of our U.S. patent rights against Mallinckrodt and MBI in Seattle," said Steven C. Quay, M.D., Ph.D., president and CEO of SONUS. "Although we fully expect MBI will again argue that they do not infringe a valid SONUS patent claim, we continue to be confident of our strong patent position, especially with the progress we are making in the patent office with the patent re-examination process. In addition, we continue to work closely with the FDA towards the approval of EchoGen(R)."

SONUS Pharmaceuticals, Inc., based in Bothell, Wash., is engaged in the research and development of ultrasound contrast agents and drug delivery systems based on its proprietary PhaseShift(TM) and fluorocarbon technology. The Company's products are being investigated to improve the diagnosis and treatment of heart disease, cancer and other debilitating conditions.

Certain of the statements made in this news release are forward looking. As discussed in SONUS' annual report on Form 10-K filed March 19, 1997, there can be no assurance that the claims in SONUS' patents will survive re-examination by the PTO or in any legal proceedings or will be ultimately enforceable. In addition, EchoGen(R) will require regulatory approval, which approval is subject to certain regulatory requirements and can be lengthy. Market Acceptance of EchoGen(R) will depend on a number of factors, including safety, efficacy, ease of administration and the presence of competitive imaging products or technologies. There can be no assurance that the FDA will approve EchoGen(R).

NOTE: SONUS Pharmaceuticals' press releases are available via PR Newswire's Company News on Call service. To receive previous SONUS press releases via fax, dial 800-758-5804, ext. 108377. SONUS releases also can be accessed on the Internet at http://www.prnewswire.com/. Additional information about SONUS can be accessed at the SONUS Home Page: http://www.sonuspharma.com/.

SOURCE SONUS Pharmaceuticals, Inc.

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/CONTACT: investors, Gregory Sessler, or media, Kelly Ford of SONUS Pharmaceuticals, Inc., 425-487-9500/

/Web site: http://www.sonuspharma.com/

(SNUS)

CO: SONUS Pharmaceuticals, Inc.; Molecular Biosystems, Inc.; Mallinckrodt,

Inc. ST: Washington IN: MTC SU:

CS-KP -- SFW031 -- 4927 01/07/98 14:40 EST http://www.prnewswire.com