This controlled feeding study investigated the adequacy of the folate RDA, 400 mcg/d as dietary folate equivalents (DFE), for Mexican American men with the MTHFR 677CC or TT genotype. Because of the interdependency between folate and choline, the influence of choline intake on folate status was also assessed. Mexican American men (n=60; 18‐55 y) with the MTHFR 677CC (n=31) or TT (n=29) genotype consumed 438 mcg DFE/d and total choline intakes of 300, 550 (choline AI), 1100 or 2200 mg/d for 12 wk. Folate status response was assessed via serum folate (SF), RBC folate, plasma total homocysteine (tHcy) and urinary folate. SF decreased (P<0.001) 66% to 7.9 +/− 0.7 nmol/L (mean +/− SEM) in men with the 677TT genotype and 62% to 11.3 +/− 0.9 nmol/L in the 677CC genotype. Plasma tHcy increased (P<0.0001) 170% to 31 +/−3 umol/L in men with the 677TT genotype and 18% to 11.6 +/− 0.3 umol/L in the 677CC genotype. At the end of the study, 34% (677TT) and 16% (677CC) had SF concentrations <6.8 nmol/L and 79% (677TT) and 7% (677CC) had tHcy concentrations >14 umol/L. Choline intake did not influence the response of the measured variables. These data show that the folate RDA is not adequate for men of Mexican descent particularly for those with the MTHFR 677TT genotype. Supported by NIH Grant #S06GM053933 and the California Agricultural Research Initiative.