The distribution of HLA-DRB1 alleles and DQB1 alleles in 100 Thai patients with non-Hodgkin's lymphoma (NHL) was analysed using the polymerase chain reaction with sequence-specific primer (PCR-SSP) method, and the association between the disease and the presence of certain HLA class II alleles was investigated. The frequencies of HLA-DRB1*1502 and DRB1*09012 were increased while those of DRB1*0404, DRB1*0803 and DRB1*1106 were decreased. On the other hand, the incidence of HLA-DQB1 alleles was similar to that in the normal population. Interestingly, only HLA-DRB1*1502 showed a significant positive association with NHL, especially in patients < or / = 45 years and in male patients. It is concluded that the DRB1*1502 allele may contribute to NHL susceptibility in the Thai population. However, further studies on the functional roles of the HLA class II alleles are necessary to elucidate NHL susceptibility.