In 10 patients with chronic renal failure treated with haemodialyses (HD) T and B cell populations were determined in peripheral blood, together with immunoglobulin concentration and NBT test in the first two hours of the procedure using cuprophan and cellulose acetate dialysers. It was found that the per cent proportions of T4, T8 and T11 were not significantly changed. The proportions of B cells with sIg, sIgG, sIgM, sIgA were not significantly altered during HD with cuprophan dialysers. The per cent of B cells with sIg, sIgG decreased significantly during HD with cellulose acetate dialysers. The per cent proportions of active and late E rosettes decreased significantly, the per cent of stable E rosettes rose significantly, while that of EAC rosettes was not significantly changed in the initial HD period with the use of both dialyser types. IgG concentration rose significantly in the initial period of HD with either dialyser, while there was no significant change in the concentration of IgA and IgM. The value of the NBT test was not altered significantly during HD with either dialyser type.