Prospective international studies have shown the incidence of post-transfusion hepatitis in the 1980s to vary between 2% and 31%. Rare cases of hepatitis B continue to occur despite donor screening for the hepatitis B surface antigen, but most are of the non-A, non-B type. Non-A, non-B hepatitis is typically mild and often subclinical in the acute phase but has a tendency to become chronic in about half the affected subjects. The recently characterised hepatitis C virus has been shown to cause most, if not all, transfusion associated non-A, non-B hepatitis. Hepatitis C seropositivity seems to be associated with viraemia and infectivity among blood donors, and donor screening for these antibodies has now been instituted in many countries. New assays now being developed are improving the sensitivity and specificity of this screening, which is estimated to prevent most cases perhaps 70 to 80% of post-transfusion hepatitis.