ABSTRACT—Sera from 111 patients with chronic viral hepatitis and from 55 cases with other liver disorders were assayed for serum inhibitory factor. The prevalence of this immunosuppressive factor was very similar between chronic hepatitis B (61%), chronic hepatitis delta (57%) and chronic hepatitis C (68%). At the same time, serum inhibitory factor was never detected in the other disorders studied. The presence of this inhibitory factor was detected in a significantly higher percentage (p<0.05) of HBeAg, HBV‐DNA positive cases (75%) than in anti‐HBe positive, HBV‐DNA negative cases (44.4%). In chronic hepatitis delta, this immunosuppressive factor was also related to HDV‐RNA positivity. The detection of this serum immunosuppressive factor in chronic viral hepatitis and its association with a high viral replication level implies a possible role of this factor in the immune pathogenic mechanism in infectious viral