Thirty-nine patients with chronic HBV infection and 38 normal persons were investigated by simultaneous assay of T suppressor cell function and enumeration of T-lymphocyte subsets by monoclonal antibodies. In patients with chronic active hepatitis B (CAH-B), T suppressor cell activity (17.8 +/- 8.8%) was significantly lower than in healthy HBsAg carriers (35.4 +/- 12.3%) and normal control persons (38.3 +/- 16.3%). The proportions of T-lymphocyte subsets in patients with CAH-B were not different from those of healthy HBsAg carriers and control persons. No correlation was observed in between percentage suppression and proportions of T-lymphocyte subsets. These findings suggest that in the absence of a simultaneous assay of function, enumeration of T-lymphocyte subsets by using monoclonal antibodies is an inadequate assessment of immune regulation.