Interest in the relationship between one-carbon metabolism (OCM) and carcinogenesis is intensifying, leading to increased use of related biomarkers as measures of exposure. Little is known, however, about the intraindividual variation in these markers and whether or not the use of a single measure is appropriate for assessing exposure-disease relationships in epidemiologic studies. We evaluated the intraindividual variation in plasma concentrations of 19 OCM biomarkers in a sample of 147 African American and 68 non-Hispanic white participants from the Southern Community Cohort Study who donated blood samples and responded to questionnaires at two time points from 2005 to 2008. Weighted kappa coefficients (κ) were calculated to assess the agreement between quartile assignments based on the repeated measures. Adjusted intraclass correlation coefficients (ICC) were also used to assess the consistency of the two measurements. Most (16/19) OCM biomarkers showed a moderate or better agreement for quartile assignment at the two time points, with only methionine, methionine sulfoxide, and cystathionine having κ ≤ 0.40. The median-adjusted ICC across the 19 biomarkers was 0.60. Reproducibility was highest for flavin mononucleotide [ICC = 0.84, 95% confidence interval (CI), 0.79-0.87] and lowest for methionine and its oxidative product methionine sulfoxide (ICC = 0.22, 95% CI 0.09-0.34; ICC = 0.20, 95% CI 0.07-0.32, respectively). Overall, the intraindividual variation in OCM biomarkers was similar for African Americans and whites and for males and females. Our results suggest that with the exception of methionine and methionine sulfoxide, OCM biomarkers generally have good intraindividual reproducibility and can be considered as reliable exposure measures in epidemiologic studies.