Twenty-eight patients (11 Caucasian, 17 black) whose blood pressure was more than 160/96 mmHg after 4 weeks on placebo added to atenolol 100 mg/day were randomly given, in addition, nisoldipine 10 mg or nifedipine 20 mg each twice a day for 8 weeks in a double-blind cross-over study. There was a statistically significant (P < 0.001) fall in blood pressure with no change in heart rate, both supine and erect, on both drugs. There were no significant differences between nisoldipine and nifedipine. Adverse effects were recorded in 15%, 17% and 35% of the patients available for safety comparison for placebo, nisoldipine and nifedipine, respectively. There were no significant differences between the black and Caucasian patients in blood pressure responses, although the study had only a low power to detect these. However, the fasting serum triglyceride levels at the end of both calcium antagonist treatment periods were highly significantly lower in the black patients compared with the Caucasian patients. Nisoldipine, which has a higher coronary vascular selectivity and less negative inotropism than nifedipine, is as effective and as well tolerated as nifedipine in patients whose hypertension is inadequately controlled on atenolol. It may have a special role in hypertensive patients with impaired left ventricular function.