We evaluated the efficacy of short-term intravenous heparin therapy in 74 patients with recent transient ischemic attacks (TIAs). The patients were treated after hospitalization until operation or long-term medical treatment was instituted. Heparin was given in a continuous infusion to maintain an activated partial thromboplastin time of 1 1/2 to 2 1/2 times control values. During the treatment period, 12 patients (16.2%) had recurrent TIAs and five (6.8%) had cerebral infarction. Bleeding complications occurred in nine patients (12.2%). In this limited series, heparin did not prevent recurrent TIAs or cerebral infarction among high-risk patients with recent TIAs.