A prospective, randomized, double-blind between-patient study was carried out to compare the efficacy and tolerance of atenolol with nifedipine and atenolol with diuretic. Ninety-eight hypertensive patients inadequately controlled after 1-month's treatment with 100 mg atenolol alone once daily received, in addition, either 20 mg nifedipine twice daily or 5 mg amiloride plus 50 mg hydrochlorothiazide once daily for a further 8 weeks. The results of blood pressure measurements in the lying and standing positions showed that the mean reduction in standing blood pressure from atenolol baseline was 28/12 mmHg for atenolol/diuretic and 18/13 mmHg for atenolol/nifedipine. The only significant difference between treatments in blood pressure control was in lying systolic blood pressure favouring atenolol/diuretic and a trend in favour of this combination for standing systolic blood pressure. Both regimens were reasonably well tolerated, although 19 patients withdrew during the course of the trial because of side-effects (2 on atenolol alone, 10 on atenolol/diuretic and 7 on atenolol/nifedipine).