Inhibitors of the angiotensin-converting enzyme (ACE) acutely increase sodium excretion. Whether or not continued treatment induces net negative sodium balance is not clear, and may depend on initial sodium balance. We therefore investigated the effects of 8 days of treatment with enalapril, 10 mg b.i.d., on sodium balance in 10 subjects with uncomplicated essential hypertension, in balance on a low (50 mmol sodium/24 h) and a liberal (200 mmol sodium/24 h) sodium intake. Sodium excretion exceeded intake during the first days of treatment, amounting to sodium losses of 101 +/- 24 and 112 +/- 15 mmol in the low and the liberal sodium diets, respectively. The sodium loss was accompanied by a fall in body weight with both regimens. The blood pressure response to enalapril was potentiated by the sodium-restricted diet. The net increase in sodium excretion after enalapril administration, however, was similar for both diets. This was particularly true for individual patients, suggesting an individual response pattern to ACE inhibition.