To explore beneficial and harmful effects of various combinations of antianginal drugs, we compared antianginal and cardiorespiratory effects of nifedipine and isosorbide dinitrate in low and high doses in combination with nadolol, a long acting beta-adrenoceptor blocker in a double-blind study in 19 patients with stable angina pectoris. Nadolol alone and in combination with the other two drugs reduced anginal attack rate and glyceryl trinitrate consumption; the high dose isosorbide dinitrate showed a further significant (P less than 0.05) reduction in both but the high dose nifedipine did not show such a trend. sigma ST depression (all leads) was significantly (P less than 0.05) more reduced by the high dose nifedipine than by the same dose of isosorbide dinitrate in combination with nadolol. Nadolol reduced forced expiratory volume in one sec (FEV1) slightly and this effect was reversed both by isosorbide and nifedipine. Isosorbide dinitrate in combination with nadolol reduced the basal and post-exercise arterial oxygen saturation (SaO2) whereas nifedipine did not reduce the mean SaO2 below the pre-trial level. A significantly greater sigma ST depression was associated with a lower post-exercise SaO2 (less than or equal to 92%) during all treatment periods but the fall of SaO2 occurred more often during isosorbide than during nifedipine treatment periods. These studies show that both isosorbide dinitrate and nifedipine enhance antianginal efficacy of nadolol. Isosorbide dinitrate, unlike nifedipine, reduces SaO2 which is associated with a greater sigma ST depression.