The purpose of this study was to test the hypothesis that urban Africans exhibit more pressor sensitivity to dietary sodium than do their rural counterparts. We studied short-term sodium sensitivity of nonrandomized representatives of rural and urban population groups in which the overall prevalence of hypertension was 7% and 24% respectively. The rural group (mean age: 39 +/- 3 years) had 20 subjects and the urban group (mean age: 37 +/- 2 years) 21 subjects. Sodium sensitivity was assessed by measuring the blood pressure response to acute dietary restriction and sodium loading. In addition, hormonal responses to the dietary sodium changes were observed. We restricted the study to normotensives. Subjects were studied on baseline diet, after 4 days of a low-salt diet providing 10 mEq sodium per day, and after 4 days of a high-salt diet providing 800 mEq sodium per day. On the high-salt diet, half of the subjects received 100 mEq supplemental potassium per day. Mean arterial pressure in rural and urban subjects increased from 79 +/- 2 to 87 +/- 2 and 82 +/- 2 to 89 +/- 2 mm Hg (+/- SEM) respectively when subjects changed from low to high salt. Pulse pressure of rural and urban subjects also increased with the high-salt diet. Potassium supplementation did not influence the pressor response. Using a 10% increase in mean arterial pressure when going from low-salt to high-salt diets as an index of sodium sensitivity, we found that 33% of urban and 35% of rural subjects were sensitive to sodium. We conclude that the sensitivities of rural and urban normotensive men to the pressor effects of sodium are not different.