Summary The efficacy of lisinopril 10-40 mg once daily was compared with that of nifedipine tablets 20-40 mg twice daily in a multicentre double-blind randomized parallel group study of 16 weeks duration involving 127 patients with mild to moderate hypertension. The groups randomized to lisinopril or to nifedipine were not significantly different with respect to any demographic variable. An analysis of the pooled data from all centres demonstrated a significantly greater fall in both lying and standing systolic blood pressure (SBP) on lisinopril than on nifedipine treatment (difference between treatments 7.70 +/- 3.34 mmHg; P = 0.02 and 10.2 +/- 3.30 mmHg; P = 0.003 for lying and standing SBP, respectively). However, this difference may be accounted for by the slightly higher mean SBP in the lisinopril treatment groups compared with the nifedipine group at the end of the placebo run-in period. Both treatments lowered lying and standing diastolic blood pressures (DBP) to the same extent and the response rates to the two treatments were the same. The effects of the two drugs on heart rate were indistinguishable from each other. There were six lisinopril and 12 nifedipine-treated patients withdrawn during randomized treatment (P = 0.22). Nineteen per cent of lisinopril patients reported an adverse event compared with 36% of nifedipine patients. The relative risk of an adverse event on lisinopril compared with nifedipine was 0.42 (confidence limits 1.027-0.172) a difference which approached statistical significance (P = 0.0573). Lisinopril produced a greater reduction in both lying and standing SBP than nifedipine and both were associated with equivalent reductions in DBP. Lisinopril may be better tolerate than nifedipine.