To assess the effects of dexamethasone on platelet function, aggregation studies were performed on nine healthy adults before and after ingestion of a single dose of dexamethasone 10 mg, and on six patients receiving daily dexamethasone. Bleeding times were done on 14 volunteers before and after a similar drug dose. Platelet aggregation by ADP, epinephrine and collagen was unchanged after dexamethasone in the healthy subjects and aggregation curves in the patient group were comparable to the normals. Bleeding times were moderatley prolonged in women (from 284 +/- 58 seconds to 389 +/- 114 seconds) but not in men. This prolongation was much less pronounced than that which occurs with low doses of aspirin and no subject experienced delayed bleeding. Dexamethasone in single high doses probably does not cuase a clinically important effect on platelet function.