Thirteen patients with mild to moderate essential hypertension and whose average supine blood pressure with no treatment was 165/104 mmHg were studied as inpatients for 3 consecutive one-week periods on different sodium intakes. On the last day of each dietary period, they received a single, 20-mg nitrendipine tablet and blood pressure was monitored every 10 minutes for 2 hours after drug administration. Nitrendipine significantly lowered blood pressure independently of the level of sodium intake, and the maximum blood-pressure lowering effect was achieved approximately 1 hour after the dose. The blood-pressure lowering effect of nitrendipine was greater on high sodium intake as compared to low sodium intake (p less than 0.02), and it was also greater with higher initial blood pressures. However, the sodium-related effect on blood pressure was, at least in part, independent of the pretreatment blood pressure. These results suggest that calcium antagonists, such as nitrendipine, are effective in reducing blood pressure in patients with essential hypertension and could be drugs of choice in those who are unable to restrict their salt intake.