Antiplatelet effects of combination therapy with aspirin and ticlopidine were investigated in comparison with single aspirin or ticlopidine therapy in 62 patients with cerebral thrombosis or transient ischemic attack. The 14, 21 and 27 patients were given orally daily aspirin 300mg, ticlopidine 200mg and aspirin 81mg with ticlopidine 100mg, respectively. Various platelet function tests were performed before and a week after medication. They included platelet aggregation (PA) to adenosine diphosphate (ADP), arachidonic acid (AA) and platelet activating factor (PAF) with turbidimetry, plasma beta-thromboglobulin (beta TG), platelet factor 4(PF4), thromboxane B2(TXB2) and 6keto-prostaglandin-F1 alpha(6keto PGF1 alpha) with radioimmunoassay, bleeding time with Simplate device, and platelet survival and lysis with Indium-111-tropolone-labelled platelets. Aspirin inhibited PA to ADP and AA but not to PAF, while ticlopidine inhibited PA to ADP and PAF but not to AA. In contrast, aspirin with ticlopidine inhibited PA to all of these agonists despite their smaller doses used. Aspirin reduced plasma TXB2 but not beta TG or PF4, while ticlopidine reduced beta TG and PF4 but not TXB2. On the contrary, aspirin with ticlopidine reduced TXB2 as well as beta TG and PF4. 6keto PGF1 alpha tended to be reduced by aspirin 300mg alone but not by ticlopidine with or without aspirin 81mg. Bleeding time was significantly prolonged by aspirin or ticlopidine alone, although most prolongation was produced by combination of aspirin and ticlopidine. Platelet survival and lysis remained unaltered in 4 patients treated with aspirin or ticlopidine alone, whereas platelet survival was prolonged and platelet lysis was reduced in 4 patients treated with both aspirin and ticlopidine.(ABSTRACT TRUNCATED AT 250 WORDS)