ABSTRACT— Immunoelectrophoresis was performed in 31 of 272 patients with chronic active hepatitis (CAH) because of an M-spike component (seven patients, 2.6%) or hypergammaglobulinemia (24 patients) revealing a monoclonal gammopathy (MG) in 11 patients. In addition, 50 randomly selected patients with CAH and no evidence for an M-spike component were tested by immunoelectrophoresis. In 13 patients (26%), an MG was found. The mean age of the 24 patients with MG was 57.4 years (range: 23–76). HBsAg was present in nine patients (37.5%), no HBV-marker was detected in ten patients (41.7%). The immunoglobulin class of MG was IgG in ten patients (41.7%), IgA in one patient (4.2%) and IgM in 11 patients (45.8%). In two patients, Bence Jones protein was found in either serum or urine. In only one patient was the MG associated with multiple myeloma, whereas none of the other 23 patients developed a malignant lymphoproliferative disease within the median observation period of 6 years. We conclude that there is an unexpectedly high prevalence of benign MG in patients with CAH.