CAMBRIDGE, Mass.
November 13, 2007

Archemix Corp., a biotechnology company focused on discovering, developing and commercializing aptamer therapeutics, today announced that it started a Phase 2a clinical trial of ARC1779, which is designed to evaluate the safety and efficacy of ARC1779 as an anti-thrombotic in patients suffering from Acute Coronary Syndrome, or ACS, undergoing emergency percutaneous coronary intervention, or PCI.

ARC1779 is an aptamer designed to bind to and inhibit the function of the protein known as von Willebrand Factor, or vWF. vWF initiates and promotes platelet clot formation in the arterial circulation of patients with ACS.

The multi-national Phase 2a trial is expected to enroll approximately 300 patients. The trial is a dose-ranging, randomized, double-blind study using ReoPro ® as a comparator. The co-primary efficacy endpoints of the trial will be the degree of myocardial perfusion and the deficit of blood supply to the working heart muscle, or myocardial ischemia, after PCI. The primary safety endpoint is bleeding, which will be measured by clinical observation. Archemix also plans to use biomarkers to measure the extent of heart damage suffered by patients as well as the activation of the clotting system.

About the ARC1779 Phase 1 Trial
The Phase 1 trial was conducted in 47 healthy volunteers and was completed in March 2007. 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 Furthermore, no serious adverse events were reported in the trial and no subject was withdrawn from the trial due to an adverse event.

About ACS
According to the American Heart Association, ACS includes a range of conditions, such as chest pain and heart attack, which are caused by insufficient blood supply to the heart due to blockages in coronary arteries, usually caused by blood clots. Patients with ACS symptoms are at significant risk for heart attack or death.

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 patent portfolio, Archemix is developing aptamer product candidates for cardiovascular and hematological diseases and cancer. In addition, Archemix has licensed its intellectual property to third parties to develop their own aptamer product candidates. 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.