Indobufen is an antiaggregatory drug which first of all inhibits platelet aggregation by interfering with cyclooxygenase enzymes in platelets. We have investigated the influence of indobufen (200 mg twice daily for 10 days) on platelet lipid peroxidation and phospholipid metabolism in diabetic patients. The production of lipid peroxidation products was significantly lower after drug treatment. Indobufen administration, however, had no influence on the fatty acid composition of platelet phospholipids.