Deep venous thrombosis (DVT) in the legs occurs in 23% to 75% of patients with acute ischemic stroke, and pulmonary embolism accounts for about 5% of deaths. New heparinoid substances, lacking the hazards of more established anticoagulants, raise the question of DVT prophylaxis for these patients. Two hundred fifty consecutive acute ischemic stroke patients were evaluated for the presence of DVT of the legs in a feasibility study for a trial of low-molecular-weight heparin prophylaxis. Forty-nine patients were found suitable for the study, of whom 11 (22.5%) developed DVT. All patients underwent clinical examination, I-125 fibrinogen leg scanning, and impedance plethysmography. Five patients were sufficiently alert and without serious neurologic deficits to justify DVT prophylaxis. Recent advances in noninvasive diagnostic techniques to detect DVT early and the development of relatively safe heparinoid compounds increase the need for a prophylactic study in patients with ischemic stroke.