Cyclosporin has been used for many years in transplantation, and in this field its role is widely documented. However, other fields of application merit to be investigated, including the role of cyclosporin in treating autoimmune hepatitis and its possible role as an antiviral agent in hepatitis C virus (HCV) infections in both immunocompetent patients and in recipients of orthotopic liver transplants. Cyclosporin A has given promising results in small studies, and experience in transplantation and other immunological disorders indicates that its side-effects can be adequately managed. Cyclosporin certainly deserves further clinical investigation for first-line therapy in autoimmune hepatitis. Cyclosporin A suppresses the HCV genome dose-dependently in vitro at clinically relevant concentrations (150-250 ng/mL). The maximum effect is similar to that obtained with IFN alpha, and the effects of these two agents are certainly additive, and possibly synergistic. The inhibitory action of cyclosporin A appears to be independent upon its immunosuppressive action. Analysis of indirect endpoints in clinical trials on cyclosporin A for immunosuppression in transplant recipients indicates that cyclosporin A treatment can delay recurrence of HCV. Small, open label studies suggest that the observed anti-HCV activity of cyclosporin A can be translated into a real clinical benefit; nevertheless, these findings need to be confirmed in randomized, controlled clinical trials.