Abnormalities of cell-mediated immunity-anergy to delayed hypersensitivity skin testing, diminished T-lymphocyte concentrations and mitogen responsiveness, and the presence of serum inhibitors--have been shown to be present in patients with portal venous obstruction and normal hepatic function. In contrast, tests of humoral immunity--antibody titiers to viral and bacterial antigens and immunoglobulin concentrations--were normal. These abnormalities in cell-mediated immunity are probably the result of the development of portal hypertension, portosystemic shunting, and congestive splenomegaly. These studies raise the possibility that qualitatively similar defects in patients with chronic liver disease and portal hypertension may, in part, be attributable to the same mechanisms.