Objective: To determine whether plasma aldosterone (PA) levels differed between African American and White prehypertensives and if so, could the difference be explained by ethnicity-related variability in urinary K⁺ and Na⁺ excretion, body mass index (BMI), and percent body fat. Design: Ethnic comparison Setting: The University of Maryland College Park and the University of Maryland School of Pharmacy. Participants: 61 (African American, n528; White, n533) prehypertensives (systolic blood pressure [SBP] 131 6 10 mm Hg, diastolic blood [DBP] 85 6 6 mm Hg). Intervention: 6-week dietary stabilization and medication tapering period. Main Outcome Measures: PA levels, Na⁺ and K⁺ excretion, blood pressure, and percent body fat and BMI. Results: We saw no differences in SBP (P5.36) and DBP (P5.54) between the two ethnic groups. PA levels were lower in African Americans compared to Whites (62 6 7 vs 107 6 12 pg/mL, P5.002). 24-hour K⁺ excretion was lower among African Americans compared to Whites (51 6 7 vs 70 6 4 mmol/day, P5.002). We saw no difference in percent body fat, BMI, SBP, or DBP between African Americans and Whites. After separately accounting for K+ excretion and Na⁺excretion and BMI, plasma aldosterone levels remained significantly different between the two ethnic groups. After adjusting for percent body fat, PA levels were not significantly different between the two ethnic groups (P5.06). Conclusions: The findings of the current study indicate that PA levels differ between African American and White prehypertensives and this difference may partly be due to ethnic variability in K⁺ excretion and percent body fat.