Purpose: The purpose of this paper was to determine whether differences in hemoglobin (Hb) and muscle aerobic capacity exist between African-American (AA) and Caucasian (CA) premenopausal women and to determine whether Hb and aerobic capacity of the muscle are associated with the racial differences in maximum oxygen uptake (V̇O2max). Methods: 43 AA and 46 CA sedentary premenopausal women were subjects. Percent body fat was determined by four-compartment model, leg lean tissue by dual energy x-ray absorptiometry, V̇O2max during a graded exercise test, aerobic capacity of the calf muscle by 31P magnetic resonance spectroscopy, and serum Hb by the cyanide method. Results: AA women had reduced V̇O2max (AA 29.3±3.0 vs CA 33.6±5.6 mL·kg-1bdw-1·min, P<0.01), reduced muscle aerobic capacity (AA 24.3±5.8 vs CA 21.3±4.8 s, P=0.01, where lower values indicate higher aerobic capacity), and reduced Hb (AA 11.8±1.3 vs CA 12.9±0.8 g·dL-1, P<0.01). The racial difference in V̇O2max persisted whether the values were unadjusted or adjusted for fat-free mass or leg lean tissue. Multiple regression analysis revealed that both Hb and muscle aerobic capacity were related to V̇O2max after adjusting for each other, race, and either fat-free mass or leg lean tissue. Being AA was associated with reduced V̇O2max in mL O2·kg leg lean tissue-1·min-1 (zero-order simple Pearson-product correlation -0.60, P<0.01). When multiple regression was used, the correlation between race and V̇O2max decreased but persisted (-0.40, <0.01) after adjusting for Hb and muscle aerobic capacity. Conclusions: These data suggest that differences in Hb and aerobic capacity of muscle are related to reduced V̇O2max in AA women. However, Hb and aerobic capacity of the muscle can only partially explain the racial differences in V̇O2max.