Ten patients with chronic stable angina pectoris and ten aged-matched healthy controls were investigated. Aspirin was given as 160 mg/day and clopidogrel as 300 mg loading dose followed by 75 mg/day. Whole blood aggregometry was performed at baseline and after 10 days with collagen or ADP as stimulator. ADP as well as collagen-induced platelet aggregation was each reduced (P<0.02) both in healthy volunteers and in patients with stable angina pectoris with combination therapy compared with aspirin only. In conclusion, treatment with clopidogrel and aspirin provides significantly greater inhibition of platelet activity than aspirin alone in patients with stable angina pectoris and in healthy control subjects.