In a cross-over double-blind trial on 15 healthy male volunteers the effect on physical exercise capacity and metabolism of single oral doses of 90 mg diltiazem or 20 mg nifedipine was compared. Both maximal physical exercise capacity and sustained exercise capacity remained unchanged after each calcium antagonist. Heart rate was higher after nifedipine but lower after diltiazem than after placebo, although the differences at the individual exercise steps were small and significant in only some. Plasma noradrenaline levels on submaximal exercise rose significantly higher after nifedipine than after diltiazem or placebo. Somatotropin, cortisol, insulin as well as carbohydrate and fat metabolic substrates were similar after the two calcium antagonists and placebo. It is concluded that short-term administration of diltiazem and nifedipine does not influence physical exercise capacity and metabolism.