Eight subjects with HBsAg-positive chronic liver disease received levamisole therapy continuously for 6 to 8 weeks. Depressed T-lymphocyte concentrations, found in all patients before therapy, transiently returned towards normal. All of the three patients who had normal delayed hypersensitivity responses before treatment showed an acute hepatitic reaction manifested by elevation of serum aspartate transaminase (AsT) and HBsAg levels, with transient cell-mediated immunity to HBsAg. This was interpreted as indicating increased lysis of infected hepatocytes. All of the five anergic patients showed no change in AsT or HBsAg levels. The clinical features and hepatic histology were unchanged. In patients with the capacity to mount normal delayed hypersensitivity responses, levamisole enhanced the cell-mediated response to HBsAg, and there was increased lysis of infected cells. Nevertheless, this treatment failed to eradicate the virus, as all patients remained HBsAg-positive.