The incidence of restenosis remains the same as initially reported (30%) and no therapeutic approach has reduced its appearance. Platelets-induced smooth muscle cell proliferation probably play a preponderant role in the pathogenesis of restenosis. The aim of this study was to evaluate the effects of ticlopidine (250 mg/day) on restenosis rate after single lesion coronary angioplasty. One hundred seventy nine consecutive patients were prospectively included in this study and were assigned to ticlopidine (group T, n = 91) or to a control group (n = 88) in an alternative fashion. Age (60 +/- 10 vs 58 +/- 9 years), gender (87% vs 87% male), treatment, coronary risk factors, lesion morphology, stenosis severity pre- and postangioplasty, type of vessel, collateral circulation, and left ventricular ejection fraction, were similar in the T and control groups, respectively. Unstable angina was more frequently found in group T patients (81% vs 65%, p less than 0.01). A late angiographic follow-up (7 +/- 2 months after angioplasty) revealed restenosis (greater than 50% luminal narrowing) in 26 patients (28%) in group T and in 21 patients (24%) in the control group (NS). At that time, 88% and 98% of patients without restenosis vs 35% and 48% of patients with restenosis were asymptomatic in the T and control groups, respectively. An exercise test prior to the late control angiogram was abnormal (angina and/or ST segment depression) in 77% and 73% of patients with restenosis in T and control groups, respectively. Thus, in our experience, ticlopidine at a dosage of 250 mg/day was unable to reduce restenosis rate after single lesion coronary angioplasty.