Heparin therapy in acute stroke is a controversial issue. It is uncertain, whether heparin has a therapeutic or preventive effect in the early phase of the stroke. From 1984-1989, 1095 patients with acute ischemic stroke were treated, 141 (12.9%) of whom received heparin within 3 days of stroke onset. The mean duration of heparin anticoagulation was 10 days. In 28 cases (20%), heparin was used as antithrombotic agent (25/28 patients suffered a basilar artery occlusion, of whom 22 died). In 113 cases (80%), heparin was used in embolic stroke to prevent recurrence (24% cardioembolic stroke, 54% arterio-arterial embolism, and 22% embolism of unknown etiology). The rate of recurrent stroke in the early phase was 13% with a persistent deficit in 5.3%. The results are comparable with those of other trials reported in the literature. Only 2 patients had an anticoagulation-related haemorrhage with clinical deterioration. Heparin anticoagulation in acute stroke is a low-risk therapy, but its preventive value has not yet been demonstrated.