Methotrexate (MTX) is a commonly used disease-modifying antirheumatic drug in rheumatoid arthritis (RA). Polymorphisms occur in several genes encoding key enzymes in the folic acid pathway, which is influenced by MTX, but have not been evaluated in patients with RA. The effect of race on allele frequency has also not been evaluated. In this study, the allele frequencies of polymorphisms in six key enzymes in the MTX-folate pathway in patients with RA and healthy controls, including several common racial groups were studied. European- and African-American patients with RA and European and African healthy controls were genotyped for 22 genetic loci in six genes in the MTX cellular pathway. Differences in genotype distributions between the different racial groups were evaluated using chi(2) tests. Allele frequencies were significantly different (p < 0.001) for eight single nucleotide polymorphisms between the European and African controls. The allele frequencies of two polymorphisms showed significant differences (p < 0.001) between the African- and European-American patients with RA. Thus, racial differences exist between the allele frequencies of several polymorphisms in enzymes in the MTX-folate pathway in patients with RA and healthy controls. Whether such differences contribute to a differential response to MTX in patients with RA deserves to be investigated.