Modern therapy with clotting factor concentrates has been dramatically successful in preventing and alleviating the worst effects of haemophilia. Before the mid to late 1980s, when effective methods of concentrate sterilization were introduced, such therapy was associated with a virtual certainty of transmission of viral hepatitis. Many patients who received intensive therapy before this time now have evidence of chronic and progressive liver disease, in which non-A, non-B agents are thought to be of dominant pathogenetic importance. Complex viral interactions involving both hepatotropic agents and HIV may occur in haemophiliacs, whose responses to infection may show atypical patterns. Interferon seems promising as a therapeutic agent. Vaccination against hepatitis B virus infection remains mandatory in patients without serological evidence of immunity.