PURPOSE--To evaluate the efficacy of diltiazem in preventing restenosis after balloon angioplasty (PTCA). METHODS--Eighty-nine patients who were undergone to successful PTCA, were divided them in 2 groups (G): A) 44 patients (50 per cent ) who received diltiazem (180 mg tid) immediately after PTCA and were kept on it for 6 months); B) 45 patients (50 per cent ) who received placebo. Fifty two lesions were dilated in GA and 54 in GB. Patients were excluded from analysis for several reasons, including: necessity of diltiazem or others calcium channel blockers use; heart failure, bradicardia, AV block of any degree, PTCA to chronic total occlusion, ostial lesions and AMI less than 30 days prior to PTCA. Patients were randomized to either the active drug or placebo in a double blind fashion. Restenosis was defined as a 50 per cent lesion. Patients underwent late angiography either at 6 months or sooner if clinically indicated. RESULTS--Both G were similar to age > 70 years (A = 7 per cent vs B = 4 per cent -p = NS), sex (A = 13 per cent vs B = 11 per cent -p = NS), stable angina (A = 43 per cent vs B = 51 per cent ), unstable angina (A = 57 per cent vs B = 49 per cent -p = NS) and single vessel (A = 91 per cent vs B = 87 per cent -p = NS) or multivessel (A = 9 per cent vs B = 13 per cent -p = NS) PTCA. We studied 39/44 (89 per cent ) patients in GA and 43/45 (96 per cent ) in GB (p = NS). We observed restenosis in 17/39 (43 per cent ) in GA and 16/43 (37 per cent ) in GB (p = NS). The restenosis rate per lesion was 39 per cent in GA and 31 per cent in GB (p = NS). CONCLUSION--Diltiazem was ineffective in the prevention of restenosis following PTCA