There is a significant decrease in the ratio of inducer (helper) to suppressor T lymphocytes in the peripheral blood of patients with primary biliary cirrhosis (PBC). These changes are not seen in other forms of cholestatic liver disease, but are similar to those described in chronic graft-versus-host disease. Cyclosporin A treatment increased the proportion of suppressor A lymphocytes and improved liver function in 6 patients with PBC. This indicates that cyclosporin A is an immunoregulatory drug. Unfortunately nephrotoxicity precluded long-term use.