Sixteen patients (5 female and 11 male, mean age 59.1 years) who had had an acute myocardial infarction within the previous 7 days, were enrolled in an open pharmacodynamic study. Patients were randomly allocated to two treatment groups and given a single subcutaneous dose of 100 or 200 mg of a new low-molecular-weight dermatan sulphate. The drug pharmacodynamic profile was determined 1, 2, 4, 6, 8, 12 and 24 h after administration. The following coagulation and fibrinolysis tests were performed: activated partial thromboplastin time, thrombin time, activated factor X inhibition, Heptest (global clotting time), heparin cofactor II affinity, functional and antigenic plasminogen activator inhibitor and fibrin plate assay. Both Heptest and heparin cofactor II affinity were significantly increased (P < 0.001) in a dose-dependent manner. The XaI was enhanced, though to a lesser extent. None of the other coagulation or fibrinolysis tests showed significant changes at either dose. Systemic and local tolerance were always very good.