Aldosterone contributes to the elevation of blood pressure (BP) by acting on the distal tubule to cause greater sodium retention and volume expansion. Blacks, in comparison with whites, have lower plasma aldosterone concentrations (PAC), possibly due to increased sodium reabsorption and resultant renin suppression, as evidenced by their lower plasma renin activity (PRA); but BP is on average higher in blacks. The seemingly different BP-PAC relationships in blacks and whites raise point to the possibility of different aldosterone sensitivity in the two race groups. Using data from a cohort of normotensive youths (n=654 observations contributed by 537 subjects), we used a varying coefficient model to examine the BP effect of PAC at different levels of PRA in blacks and whites. We characterized the effects of PAC as a function of PRA and assessed its effect on age, sex, and height-adjusted BP percentile. The estimated effects are presented graphically (Figure 1 a&b). Blacks had lower PRA and PAC (PRA: 2.8 vs 3.3, p=0.002; PAC: 8.7 vs 14.1, p<0.0001; PAC/PRA: 4.7 vs 5.4, p=0.172), and marginally higher systolic and diastolic BP percentiles (SBP%: 44.5 vs 40.6, p=0.082; DBP%: 57 vs 51, p=0.004). In blacks, the BP effect of PAC was much greater in blacks at lower PRA levels (p=0.004); in whites, PAC effect on BP was not significant (p=0.164) and the effect did not change noticeably with PRA. In conclusion, the finding supports the notion that blacks have higher levels of aldosterone sensitivity, especially for those with lower PRA. A sustained state of volume expansion appears to make blacks vulnerable to the BP effects of even small increments in sodium retention produced by aldosterone.