This study aims to investigate the association between the polymorphic loci of ABCB1 gene 3435C/T, MTHFR gene 677C/T and 1298A/C, and the susceptibility to RA as well as its serological subtypes (ACPA-positive, RF-positive) in the population of Gansu region, China. The gene discussed is ABCB1; the disease is rheumatoid arthritis.