A total of 45 patients with severe psoriasis vulgaris treated with Methylaminopterin NFN (Methotrexate Lederle) were HL-A typed in order to seek a possible correlation between HL-A antigens and the histological abnormalities in post-Methotrexate (MTX) liver biopsies. Highly significantly increased frequencies of w17 and TY (P less than 0.0001) were found, while HL-A13 Was only slightly increased. No statistically significant correlations were found between HL-A antigens and liver histology. HL-A typing does not seem to be of any predictive value in the pre-MTX screening of psoriatics in order to rule out patients with a high risk of liver damage during long-term MTX therapy.