Following tests for evaluation, patients are hospitalized for 14 days. They are admitted to the hospital in the afternoon and, starting the next morning, receive a continuous infusion of dextran sulfate through an intravenous line for 14 days. The infusion is adjusted to maintain an activated partial thromboplastin time (APTT) of 50 to 65 seconds. Blood is withdrawn 5 times on the first day that patients receive dextran sulfate and at least once a day thereafter for safety. Patients' clinical condition, blood clotting, and blood platelets are monitored very closely.