Clinical trials have shown that antiplatelet agents are effective in the prevention of thrombosis in arterial diseases and increase bleeding time. To compare the effects of three such drugs [acetylsalicylic acid (ASA) at two dose levels, ticlopidine and indobufen] on bleeding time, we performed a randomized cross-over study on 12 normal subjects. All received the four treatments (ASA 300 mg daily and 500 mg twice daily, ticlopidine 250 mg twice daily and indobufen 200 mg twice daily, each for 6 days plus one dose on day 7) in a sequential manner with a washout period of 15 days between the treatments. Bleeding time was measured using a Surgicut device (Ortho, Milan, Italy) before treatment, 2 and 24 h after the first administration, and before and 2, 24, 48 and 72 h after the last administration. ASA (at both doses) and indobufen quickly induced a significant prolongation of bleeding time, but the effect of indobufen soon wore off after the treatment was stopped, unlike that of ASA. In contrast, ticlopidine treatment prolonged bleeding time only after the first 24 h, and after 7 days the mean value was significantly higher than with ASA (both doses) and indobufen. This significant difference in bleeding time between ticlopidine and the other drugs was still present 48 h after the end of treatment.