Changes of T and B lymphocyte populations have been studied in chronic active hepatitis and liver cirrhosis. It was found that E rosette-forming T lymphocyte counts were significantly lower in this group of diseases than in the controls. The B cell count did no change significantly as compared to the controls. Incubation with levamisole was followed by a significant increase in active E rosette-forming and total T-cell counts. The authors have appraised the experimental results by comparison to published findings.