HLA-DRB1 allele typing was performed by the PCR-RFLP method on 59 ulcerative colitis (UC) patients and 136 healthy controls. Phenotypic frequencies of HLA-B52 and DR2 were significantly increased among the UC patients, serologically. DNA typing of HLA-DRB1 revealed that the genotypic frequency of DRB1*1502 was higher in UC than in the controls (49.2% vs 17.6%; P < 0.0001). In the analysis of clinical parameters, 82.8% of patients bearing DRB1*1502 were treated with corticosteroids. DRB1*1501 and DRB1*1502 differ in only one amino acid at residue 86 (valine vs glycine), and 66% of the UC patients carried two glycines at position 86 in the HLA-DR beta-chain (vs 51% of control; P < 0.05). These observations suggest that the presence of Gly-86 in the HLA beta-chain and surrounding amino acid sequence of HLA-DRB1*1502 is strongly associated with susceptibility to UC.