To study the relation between general cellular immunity and the course of hepatitis B within a group of chronic hemodialysis patients, T-lymphocyte number and function were investigated in 13 persistently hepatitis B surface antigen (HBSAg)-positive patients, in 32 HBSAg-negative patients, and in 11 patients who had recovered from hepatitis B and compared with that of 21 age-matched controls. Phytohemagglutinin-induced lymphocyte stimulation in vitro and the number of circulating T-cells in the HBSAg-positive group were significantly decreased as compared with those of the recovered group and the controls. Lymphocyte stimulation by pokeweed mitogen and by an antigen cocktail showed the same tendency, but no significant differences between the HBSAg-positive and the recovered groups. Uremic sera from the three patient groups had similar depressive effects on phytohemagglutinin induced lymphocyte stimulation of controls. Serum immunoglobulin G, (IgG), IgA, and IgM were normal in the three patient groups. It is concluded that chronic hemodialysis patients, who have become persistent HBSAg-carriers, have a significantly decreased T-lymphocyte number and function as compared with hemodialysis patients who are able to eliminat hepatitis B virus (HBV). The difference could not be ascribed to the HBV infection itself. This indicates that T-cells play an important role in the elimination of HBV in hemodialysis patients.