Seventy-five patients (28 HBsAg-positive and 28 HBsAg-negative) with chronic active hepatitis (CAH) were studied for HLA antigens. In the whole material, the HLA antigens were distributed as in the controls, with the only exception of the HLA-A9 antigen, the frequency of which, as compared with the controls, was moderately increased (37.4% against 22.7%). It was mainly the HBsAg-negative group which showed a significant increase in the frequency of the HLA-A9 antigen (42.9%). In the HBsAg-negative group, as compared with the HBsAg-positive group, where the frequency of HLA-A2 was 53.2%--and as compared with the controls, too--it was relatively low 29.3%. The frequency of HLA-A1 and HLA-B8 was not increased in any type of chronic active hepatitis. HLA-B8 was less frequent in the HBsAg-positive than in the HBsAg-negative group (10.6% against 21.4%).