A patient with lymphosarcoma treated with weekly injections of vincristine developed an acute myocardial infarction immediately after the second injection of vincristine. After he recovered from the infarction, the treatment was continued and he developed an additional myocardial infarction. In vivo and in vitro studies have not revealed any effect of vincristine on the clotting mechanism. The possible causes for the association of vincristine-treated lymphoma and myocardial infarction are discussed.