CAMBRIDGE, Mass.
April 22, 2008

Archemix Corp., a biotechnology company focused on discovering, developing and commercializing aptamer therapeutics for rare hematological diseases, announced that ARC1779 has received orphan drug designation from the U.S. Food and Drug Administration. ARC1779, a novel aptamer therapeutic, is a first-in-class anti-platelet agent for the treatment of a rare, life-threatening blood disorder known as thrombotic thrombocytopenic purpura, or TTP. There is no drug approved for the treatment of TTP and acute episodes of TTP are associated with a significant mortality rate, estimated to be as high as 20 percent.

ARC1779 is currently in Phase 2 clinical development with a clinical trial designed to assess the safety, pharmacokinetics and pharmacodynamic effects of ARC1779 in approximately 28 patients with vWF-mediated platelet function disorders, including acute TTP.

"The designation of ARC1779 as an orphan drug underscores the importance of developing effective treatments for patients with TTP," said Errol DeSouza, President and Chief Executive Officer, Archemix. "To date we have been encouraged by ARC1779's early-stage clinical results, and we continue to believe it has the potential to offer a new and effective treatment in a disease for which there is currently no drug therapy available."

ARC1779 is designed to bind to and inhibit a protein known as von Willebrand Factor (vWF) that protects the body from bleeding and blood clots and, therefore, the administration of ARC1779 potentially increases or restores platelet counts to normal levels reducing or eliminating the formation of blood clots that cause the morbidity and mortality associated with acute episodes of TTP. Patients suffering an acute episode of TTP experience widespread clotting and the resulting restriction of blood flow to critical organs such as the brain, kidneys and heart, which may cause strokes, seizures, kidney failure or heart attack.

About The Orphan Drug Act
The Orphan Drug Act of 1983 allows the FDA to grant orphan drug status to novel drugs or biologics that treat a rare disease or condition affecting fewer than 200,000 patients in the U.S. The Orphan Drug Act provides the drug developer with several financial benefits and incentives related to the orphan drug, including tax credits for clinical research costs, ability to apply for annual grant funding, clinical research trial design assistance, waiver of Prescription Drug User Fee Act (PDUFA) filing fees, and a seven-year period of U.S. marketing exclusivity if the drug is the first of its type approved for the specified indication.

About TTP
Thrombotic thrombocytopenic purpura, or TTP, is a rare blood disorder that arises from uncontrolled activation of von Willebrand Factor (vWF), a protein which under normal conditions plays a key role in maintaining the normal balance between bleeding and clotting. In patients suffering from TTP, vWF binds excessively to platelets, causing excessive blood clots. These clots form throughout the circulation and can lead to serious medical consequences such as strokes, seizures, kidney failure and heart attack. Each year in the United States, between four and 11 new cases of TTP per million of the total population are diagnosed. There is no approved drug treatment for patients with TTP.

About ARC1779
ARC1779, a pegylated aptamer consisting of 40 nucleotides, is Archemix' lead product candidate for the treatment of TTP. ARC1779 is designed to inhibit the function of a protein called von Willebrand Factor, or vWF, which is, when activated, responsible for the adhesion, activation and aggregation of platelets.

In a Phase 1 trial conducted in 47 healthy volunteers, intravenous administration of ARC1779 demonstrated dose- and concentration-dependent inhibition of plasma vWF activity and platelet function. Furthermore, no serious adverse events were reported in the trial and no subject was withdrawn from the trial due to an adverse event. The key results of this trial were presented at the 2007 annual meeting of the American Heart Association, and were published in full in the journal Circulation in December, 2007.

About Aptamers
Aptamers are synthetically-derived oligonucleotides, or short nucleic acid sequences, that bind to protein targets with high affinity and specificity and can be designed to have a specified duration of action. Aptamers represent an emerging class of potential therapeutic agents that Archemix believes may have broad application to treat a variety of human diseases.

About Archemix
Archemix is a biotechnology company focused on discovering, developing and commercializing aptamer therapeutics. Using Archemix's proprietary processes for discovering aptamers, which are protected by its broad patent portfolio, Archemix is developing aptamer product candidates for rare hematological diseases. In addition, Archemix has licensed its intellectual property to third parties to develop their own aptamer product candidates. Currently, Archemix and its licensees are evaluating five different aptamer product candidates in human clinical trials; three in Phase 2 and two in Phase 1. To date, Archemix has licensed its intellectual property to discover and develop aptamer product candidates to nine biotechnology and pharmaceutical companies, including Pfizer, Merck Serono, Takeda Pharmaceuticals and Elan Pharma.