Increased sodium (Na(+)) retention in blacks could be related to the high prevalence of hypertension in adult blacks. Na(+) retention in response to controlled dietary Na(+) has not been rigorously compared in the different race groups. The present study assessed Na(+) retention in 22 black and 14 white girls, 11-15 yr old, during 3 wk on a low (1.3 g, 57 mmol)- and during 3 wk on a high (4 g, 172 mmol)-Na(+) diet in a randomized order, crossover design. Subjects were matched by postmenarcheal age and weight. After a 1-wk equilibration period, the mean daily Na(+) retention was 357 +/- 69 mg (15.5 +/- 3.0 mmol) in blacks and 239 +/- 37 mg (10.4 +/- 1.6 mmol) in whites on the low-Na(+) diet and 991 +/- 138 mg (43.1 +/- 6.0 mmol) in blacks vs. 334 +/- 90 mg (14.5 +/- 3.9 mmol) in whites (P < 0.001) on the high-Na(+) diet. The greater Na(+) retention in blacks was not accompanied by an increase in fecal or sweat Na(+) excretion. Blood pressure and weight did not increase despite the Na(+) retention, and thus, the retained Na(+) appeared to reside in a nonextracellular compartment that we speculate to be bone. In summary, black girls showed greater Na(+) retention compared with white girls. The difference in Na(+) handling may contribute to underlying racial differences in susceptibility to hypertension.