The cardiovascular effects of single oral doses of nifedipine (5 and 10 mg) and nicardipine (20 and 30 mg) were compared in a placebo controlled double-blind crossover study involving 8 healthy male volunteers. Two hours following drug administration stroke volume and cardiac index were measured non-invasively using transthoracic electrical bioimpedance cardiography during passive tilting, graded bicycle exercise, and recovery from exercise. Two separate experiments were performed in the absence of active drug to allow the reproducibility of the measurements to be assessed. Coefficients of variation (within experiment/between experiments) for cardiac index were 7.0%/19.9% at rest and 11.5%/9.3% at 180 W exercise. Both nifedipine and nicardipine increased stroke volume and cardiac index and reduced total peripheral resistance (mean blood pressure/cardiac index) at all times in the experiment. Reductions in peripheral resistance were similar for nifedipine 10 mg and nicardipine 20 mg but in these doses slightly larger increases in heart rate were produced by nifedipine, and in stroke volume and cardiac index with nicardipine. The study shows that the cardiovascular effects of nifedipine and nicardipine can be detected using impedance cardiography which is a simple, safe, and inexpensive technique. The differences between the effects of the two drugs were small. Although some were of statistical significance and are consistent with a less marked cardiodepressant effect for nicardipine, the clinical importance of these observations is uncertain. Further studies to examine the effect of oral nifedipine and nicardipine in patients with impaired ventricular function may be helpful in clarifying this tissue.