Aldosterone influences the kidney's normal regulation of blood pressure (BP), but if consistently elevated, aldosterone may contribute to hypertension. BP is decreased with aerobic exercise training (AEX), but the extent to which plasma aldosterone (PA) levels change is unclear. The CYP11B2 -344C/T polymorphism has been associated with hypertension and may contribute to the change in BP and PA with AEX. The purpose of this study was to determine if 6 months of AEX changed PA levels, 24-hour Na+ excretion and BP in middle-aged to older prehypertensives, and whether the -344C/T polymorphism was associated with changes in these primary outcome variables. Forty (23 Caucasians, 14 African descents (AD), 2 Asian/Pacific Islanders and 1 of other ethnicity) disease free sedentary prehypertensives completed AEX. All participants followed the AHA Step I diet. Blood samples were collected under fasting and supine conditions and PA was measured by RIA. In the total sample, PA levels decreased after AEX (p=0.04). The reduction in PA levels in Caucasians (-37±15 pg/ml, p=0.02) tended to be greater (p=0.07) than the reduction in PA levels in AD (-2±8 pg/ml, p=0.77). Among AD, PA levels tended to decrease when controlling for baseline PA levels (p=0.09). The change in systolic BP (SBP) in Caucasians (-3±1 mm Hg, p=0.05) was significantly different (p=0.03) than the change in SBP in AD (4±3, p=0.28). In the AD, 24-hour Na+ excretion tended to increase when controlling for baseline 24-hour Na+ excretion (p=0.06). Among the Caucasians, the TC+CC genotype group tended to decrease PA levels (-39±21 pg/ml, p=0.09) and significantly decreased SBP (-4±2 pg/ml, p=0.03). Among AD, the TT genotype group significantly decreased PA levels when controlling for baseline PA levels (-17±7 pg/ml, p=0.04). The AD TC+CC genotype group tended to increase SBP when controlling for the change in 24-hour Na+ excretion (11±2 mm Hg, p=0.09) and 24-hour Na+ excretion significantly increased when controlling for the change in BMI (14±11 mmol/d, p=0.03). BP and PA levels appear to be more responsive to AEX in Caucasians compared to AD. The CYP11B2 -344C/T gene appears to influence the responses of hypertensive phenotypes to AEX.