Since November 1989, the Japan Red Cross has been screening blood donors for hepatitis C virus antibody (anti-HCV) with 1st generation assay and high-titer antibody to hepatitis B virus core antigen (HBcAb). To clarify the effectiveness of the new screening tests for the prevention of post-transfusion hepatitis, the incidence of post-transfusion hepatitis after the introduction of new tests (December 1989 to September 1990) was compared with the incidence before the in introduction (January 1982 to December 1987). The incidence of "definite" post-transfusion hepatitis was 10.3% (205/1991) with a mean transfusion volume of 10.2 units before the screening, and 3.9% (11/282) with a mean transfusion volume of 14.6 units after the introduction of the new screening tests. Statistical analysis revealed a significant decrease of post-transfusion non-A, non-B hepatitis after the introduction of new tests (chi 2 = 10.9, P < 0.01). The incidence of "probable" post-transfusion hepatitis was 12.4% (246/1991) and 11.7% (33/282) respectively. No significant change was observed between the rates of "probable" post-transfusion hepatitis before and after the introduction of the new tests. It was concluded that anti-HCV and high-titer anti-HBc screening of volunteer blood donors could contribute to the prevention of the post-transfusion non-A, non-B hepatitis in Japan.