Rheumatoid arthritis (RA) in a Thai population is significantly associated with HLA-DR4. The frequency of DR4 was 43 per cent in RA patients and 20 per cent in the healthy controls (p = 0.00008, OR = 3.06, 95% CI = 1.71, 5.52). To analyze which DR4 alleles were associated with the disease, the authors subtyped 52 DR4-positive RA patients compared to 28 DR4-positive healthy controls by amplification with DR4-specific primers followed by direct sequencing. Six DR4 alleles (DRB1*0401, *0403, *0404, *0405, *0406, and *0410) were found in the RA patient group while 5 alleles (DRB1*0401, *0403, *0405, *0406, and *0407) were found in the control group. Both groups were predominated by DRB11*0405, but there was a significant increase in the frequency of DRB1*0405 in DR4+ RA patients compared to DR4+ healthy controls (84.6% vs 46.4%, p = 0.0008, OR = 6.35, 95% CI = 1.96, 21.08). DR4 which shared epitope alleles (DRB1*0401, *0404, *0405) were observed in 47 (90.3%) DR4+ patients and 15 (53.5%) DR4+ controls (p = 0.0005, OR = 8.15, 95% CI = 2.29, 33.2). In addition, the authors found that DRB1*0403 was significantly decreased in DR4+ RA patients compared to controls (p = 0.0065, OR = 0.07, 95% CI = 0, 0.67).