The adhesiveness of platelets to collagen and glass was studies ex vivo in groups of patients with ischemic heart disease (IHD) and acute myocardial infarction (AMI). Adhesiveness was increased to glass and normal collagen in both groups of patients. No relation was found between reinfarction rate and adhesiveness in the acute stage of AMI. Electrophoretic mobility of platelets was the same in the AMI patients and a normal control group. It suggested that the increased 'retention' of platelets in IHD patients might be due more to platelet hyperaggregation or to hypersensitivity to platelet aggregating agents than to altered adhesiveness.