The interindividual variability of the blood pressure response to changes in dietary sodium intake might be traced in part to heterogeneity in renal adaptation. To further explore this possibility, we evaluated glomerular filtration rate and tubular sodium handling in 47 healthy male volunteers from the Olivetti factory in Naples who were studied on their habitual sodium-rich diet (urinary sodium, 184 +/- 9 mmol/24 h) and after 3 days of a salt-restricted diet (urinary sodium, 69 +/- 5 mmol/24 h). Individual salt sensitivity, defined as the mean blood pressure change recorded after the shift from habitual to low sodium diet, significantly and directly correlated with glomerular filtration rate and absolute proximal sodium reabsorption during the habitual diet. When the entire population was divided into tertiles of salt sensitivity, the group with the highest salt sensitivity showed higher blood pressure, glomerular filtration rate, and absolute proximal sodium reabsorption during the habitual diet compared with the least salt-sensitive group; however, during the low NaCl diet, no differences were detectable between the groups. Twenty-four-hour urinary sodium was similar across the groups. We conclude that relative hyperfiltration and altered tubular sodium handling may occur in salt-sensitive normotensive individuals on a high sodium diet and that NaCl restriction may offset these abnormalities.