Angiotensin converting enzyme (ACEi) inhibition retards renal function loss, but the therapeutic benefit varies between individuals. Renoprotection is poor in patients with the ACE DD genotype. ACE genotype is reported to affect short-term antiproteinuric response to ACEi, a predictor of long-term renoprotection, in some studies but not in others. Short-term responses to ACEi are enhanced by stimulating the renin-angiotensin system, that is, sodium restriction. We hypothesized that the ACE genotype influences sodium dependency of the response to ACEi. Therefore, we performed a cross sectional analysis of short-term responses to ACEi (enalapril or lisinopril) in 88 patients with stable non-diabetic proteinuria (> 1.0 g/day) and variable sodium intake. ACE genotype distribution was: DD, N = 25; ID, N = 40; II, N = 23. Baseline proteinuria (5.9 +/- 0.7; 5.8 +/- 0.07; 4.8 +/- 0.8 g/day, respectively) and mean arterial pressure (108 +/- 3; 106 +/- 2; 107 +/- 2 mm Hg, respectively) were similar for the three genotypes. ACEi similarly reduced proteinuria (-49 +/- 5; -55 +/- 4, -48 +/- 6%, respectively) and blood pressure (-12 +/- 3; -14 +/- 1 and -12 +/- 2%, respectively) in the three groups. Interestingly, the responses to ACEi of proteinuria (r = 0.42, P < 0.05) and blood pressure (r = 0.41, P < 0.05) correlated with urinary sodium excretion in DD genotype but not in the ID (r = 0.05 and 0.17, resp) or II genotype (r = 0.09 and 0.08, respectively). Thus, in the DD group, individuals with a high sodium excretion had a less effective response to ACEi. We conclude that differences in sodium status could account for disparities between studies on the relationship between ACE genotype and response to ACEi, and that sodium restriction might be a strategy to circumvent treatment resistance in the DD genotype.