We compared the effects of abrupt cessation of nifedipine and isosorbide dinitrate therapy in patients with stable angina pectoris. Eighteen males were studied. Each patient received isosorbide dinitrate and nifedipine continuously for 5 weeks by randomised cross-over technique. Exercise treadmill tests were performed before each treatment period, at the beginning of treatment, 4 weeks after initiation of treatment and on the first and eighth days of drug withdrawal. At the end of treatment the antianginal effect of both agents attenuated (versus acute administration). Abrupt cessation of isosorbide dinitrate caused only a tendency towards decrease in exercise tolerance versus pre-treatment level. Alternatively, abrupt cessation of nifedipine resulted in substantial deterioration in exercise tolerance, which was statistically significant 21 and 24 h after the last dose administration. The number of anginal attacks increased >25% in two patients after cessation of isosorbide dinitrate and in eight patients after cessation of nifedipine. In no patient rest angina episodes appeared after stopping of isosorbide dinitrate, however, after stopping of nifedipine rest angina episodes appeared in three patients. We conclude that withdrawal phenomenon of nifedipine is much more pronounced than that of isosorbide dinitrate and may emerge on the first day of drug cessation. Such a phenomenon may be evident even in patients in whom nifedipine effect have attenuated due to the development of tolerance.