To evaluate the efficacy of recombinant interferon alpha-2b in the treatment of patients with acute post-transfusion hepatitis C, a randomized controlled trial was conducted in 33 acute post-transfusion hepatitis C patients; 16 patients received 3 million units of subcutaneously injected recombinant interferon alpha-2b 3 times a week for 3 months and 17 patients without specific treatment were used as controls. At the end of the interferon treatment, 13 (81%) patients in the interferon-treated group normalized serum alanine aminotransferase compared with only six (35%) patients in the control group (p < 0.01). One year after completion of the interferon treatment, nine (56%) patients in the interferon-treated group and six (38%) patients in the control group normalized serum alanine aminotransferase (p = 0.35). Serum HCV-RNA measured by reverse transcription-polymerase chain reaction was positive in all patients at the time of enrollment and then became undetectable in 13 (81%) patients in the interferon-treated group and two (12%) patients in the control group at the end of interferon treatment (p < 0.001). One year after completion of the interferon treatment, seven (44%) patients in the interferon-treated group and two (13%) patients in the control group had persistent undetectable serum HCV-RNA (p = 0.08). Using a logistic regression model, the lower pretreatment level of serum HCV-RNA measured by quantitative branched DNA signal amplification assay was the only predictor for a favorable response to the interferon treatment in acute hepatitis C patients.(ABSTRACT TRUNCATED AT 250 WORDS)