Histocompatibility antigens have been studied in 328 uraemic patients treated by chronic haemodialysis, of whom 201 were contaminated by hepatitis-B virus associated antigen (HBs Ag). The frequency of the phenotypes HL-A 1 (36.2%), HL-A 8 (29.8%) and the HL-A 1,8 (23.4%) was significantly higher in the group of 47 patients who were able to eliminate HBs Ag after a transient antigenemia, than in the group of 154 patients who became chronic carriers of this antigen (P less than 0.01 for HL-A 1,8 association). These frequencies were also higher than the corresponding ones in the normal French population (P less than 0.01 for HL-A 8; P less than 0.001 for HL-A 1,8 association). In contrast, the HL-A frequencies observed in the group of patients with persistent antigenemia were not different from those observed in healthy controls. In conclusion, the presence of HL-A 1,8 phenotype seems to be correlated, in uraemic haemodialyzed patients, with a better immunological response against hepatitis B virus and hence, with the ability to elminate HBs Ag.