We examined HLA-A,B,C and DR locus antigens in 38 Japanese patients who had recovered from halothane hepatitis. The patients were divided into two subgroups, i.e. jaundice and non-jaundice groups, because the clinical features were quite different in each. DR2 was positive in 14 (58.3%) of 24 patients with jaundice, compared with 281 (33.6%) of the 837 Japanese healthy controls (chi-square with Yates' correction = 5.30, relative risk = 2.77, P less than 0.025). Conversely, Bw44 was increased in non-jaundice patients (50.0%), compared with 157 (12.7%) of the 1234 Japanese healthy controls (chi-square with Yates' correction = 13.75, relative risk = 6.86, P less than 0.001). The haplotype frequency (Hf) of Aw24-Bw52-DR2 was high in the patients with jaundice (Hf = 0.2362), while it was zero in the patients without jaundice (P less than 0.0042). These data suggest that the two groups of halothane hepatitis have different genetic backgrounds.