The response of peripheral blood T lymphocytes to concanavalin A (Con A) assessed by the production of leukocyte migration inhibitory factor (LMIF), was studied in patients with acute viral hepatitis type B and in patients with chronic aggressive hepatitis carrying hepatitis B surface antigen (HB_sAg). Lymphocytes from patients in the acute period of the disease and in severely active chronic aggressive hepatitis showed the ability to respond by LMIF production while lymphocytes from patients with moderately active chronic aggressive hepatitis were unable to do so. In parallel, it was shown that lymphocytes from the latter group of patients were capable of suppressing Con-A-induced LMIF production. Thus, mitogen-induced mediator production may be a useful parameter in the further characterization of chronic viral hepatitis.