Population-based studies report differences in folate status indicators among Mexican American (MA), African American (AA) and Caucasian (CA) women. It is unclear, however, whether these differences are due to variations in dietary folate intake. The present study was designed to investigate the influence of ethnicity/race on folate status parameters in MA, AA, and CA women (18-45 y; n = 14 in each group) under conditions of strictly controlled folate intake. In addition, the adequacy of the 1998 folate U.S. recommended dietary allowance (RDA), 400 micro g/d as dietary folate equivalents (DFE), for non-Caucasian women was assessed. Subjects (n = 42) with the methylenetetrahydrofolate reductase 677 CC genotype consumed a low-folate diet (135 micro g DFE/d) for 7 wk followed by repletion with 400 (7 MA, 7 AA, 7 CA) or 800 micro g DFE/d (7 MA, 7 AA, 7 CA) for 7 wk. AA women had lower (P </= 0.05) blood folate concentrations and excreted less (P </= 0.05) urinary folate throughout folate depletion and repletion with 400 and/or 800 micro g DFE/d compared with MA and/or CA women. MA women had lower (P </= 0.05) plasma total homocysteine (tHcy) throughout folate depletion and during repletion with 400 micro g DFE/d relative to the other ethnic/racial groups. Repletion with the 1998 folate U.S. RDA led to normal blood folate and plasma tHcy for all 3 ethnic/racial groups. Collectively, these data demonstrate that ethnicity/race is an important determinant of folate status under conditions of strictly controlled dietary folate intake and support the adequacy of the 1998 folate U.S. RDA for the 3 largest ethnic/racial groups in the United States.