Acusphere Reaches 700 Patient Enrollment Mark in AI-700 Phase 3 Trials.

WATERTOWN, Mass. -- Acusphere, Inc. (NASDAQ:ACUS) today announced that it has cumulatively enrolled 700 patients in the pivotal Phase 3 clinical program for AI-700, its lead product candidate. AI-700 is a cardiovascular drug designed to enable ultrasound to compete more effectively with nuclear stress testing, currently the leading procedure for detecting coronary heart disease. The Company also announced that it has instructed clinical sites in one of its two concurrent pivotal trials in this program, the "32" trial, to suspend further patient enrollment because the Company believes that it has enrolled a sufficient number of patients in that trial for the results to be able to achieve statistical significance.

Acusphere's Phase 3 trials for AI-700 are designed to demonstrate that stress echo with AI-700 is comparable to nuclear stress testing in the detection of coronary heart disease. The number of patients estimated by the Company to be required in these trials and achieve statistical significance is based upon a variety of assumptions, the majority of which are derived from the Company's prior trials. Before formally completing either the 32 or 33 trial, the Company has elected to have an independent data monitoring board review the trial data and confirm that the number of patients currently enrolled will provide statistically significant information. This independent review has the additional benefit of enabling the Company to make enrollment adjustments, if necessary, before formally closing out the trials. The Company anticipates receiving this information in the first quarter of 2006.

While awaiting the independent review of the Phase 3 trial data, Acusphere is continuing to enroll patients in the 33 trial. In the 32 trial, where enrollment has been suspended, the 90-day follow-up period has begun on the last patient enrolled.

"We are very pleased to have enrolled 700 patients in these trials earlier than we had expected, and we are hopeful that both Phase 3 trials can be completed soon. Given the substantial resources Acusphere has invested to arrive at this stage and the importance of achieving statistical significance in both trials, we believe that it is prudent to do everything we can to ensure that an adequate number of patients are enrolled in the trials. Therefore, an independent data monitoring board will review the data from the pivotal trials and confirm our estimates before we close-out the trials," commented Sherri C. Oberg, President and CEO of Acusphere. "We plan to provide a public update on the findings of this review when they are available."

About Acusphere, Inc.

Acusphere (NASDAQ: ACUS) is a specialty pharmaceutical company that develops new drugs and improved formulations of existing drugs using its proprietary microparticle technology. Acusphere's three initial product candidates are designed to address large unmet clinical needs within cardiology, oncology and asthma. These product candidates were created using proprietary technology that enables Acusphere to control the porosity and size of nanoparticles and microparticles in a versatile manner that allows particles to be customized to address the delivery needs of a variety of drugs. Acusphere's lead product candidate, AI-700, is a cardiovascular drug in Phase 3 clinical development. AI-700 is designed to enable ultrasound to compete more effectively with nuclear stress testing, the leading procedure for detecting coronary heart disease. An estimated 10.7 million procedures are done each year in the U.S. to detect coronary heart disease, the leading cause of death in the United States. For more information about Acusphere visit the Company's web site at www.acusphere.com.

This Release contains forward-looking statements which are made pursuant to the safe harbor provisions of Section 21E of the Securities Exchange Act of 1934. Investors are cautioned that statements in this press release, including statements relating to AI-700 regarding the number of patients needed to complete the pivotal trials, the timing of data release, and the probability that previous AI-700 trial performance may be indicative of future AI-700 clinical trial success, constitute forward-looking statements which involve risks and uncertainties. The Company's actual results may differ materially from those anticipated in these forward-looking statements based upon a number of factors, including anticipated operating losses and existing capital obligations, uncertainties associated with research, development, testing and related regulatory approvals, including uncertainties regarding the ultimate outcome of Acusphere's Phase 3 clinical trials for AI-700 and uncertainties regarding the number of patients required to complete the Phase 3 clinical trials, uncertainties regarding the cost, timing and ultimate success of the build-out of the Company's commercial manufacturing facility, including qualifying such facility in accordance with applicable regulatory requirements, unproven markets, future capital needs and uncertainty of additional financing, competition, uncertainties associated with intellectual property, complex manufacturing, high quality requirements, lack of commercial manufacturing experience, dependence on third-party manufacturers, suppliers and collaborators, lack of sales and marketing experience, loss of key personnel, uncertainties associated with market acceptance and adequacy of reimbursement, technological change and government regulation, and other risks and challenges detailed in the Company's filings with the U.S. Securities and Exchange Commission, including the Company's Quarterly Report on Form 10-Q for the quarter ended September 30, 2005. Readers are cautioned not to place undue reliance on any forward-looking statements, which speak only as of the date of this Release. The Company undertakes no obligation to publicly release the results of any revisions to these forward-looking statements that may be made to reflect events or circumstances that occur after the date of this Release or to reflect the occurrence of unanticipated events.