We report the case of a 51-year-old renal transplant patient, treated by interferon alpha (5MUI, three times a week) since he presented a coinfection by hepatitis B (HBV) and hepatitis C (HCV) virus for more than 7 years, associated with a chronic increase in serum alanine aminotransferase (ALT) levels and a chronic active hepatitis. The 4-month treatment was associated with a sustained normalization of ALT, a disappearance of HBV replication and a transient clearance of HCV viremia. Side effects were moderate and included thrombopenia (90,000/mm3), leucopenia (2200/mm3), an increase in serum creatinine (178 mumol/l). The withdrawal of alpha interferon was associated with the correction of these parameters. No rejection was observed on kidney biopsy. Meanwhile, liver histology was not affected by the treatment. To date, nineteen months after the end of alpha interferon therapy HBV DNA was still negative; ALT remained normal despite the early recurrence of HCV viremia; this emphasized the fact that HBV infection was certainly the most important factor involved in the patient's chronic hepatitis. It is concluded that alpha interferon therapy is able to decline HBV replication for a prolonged period in renal transplant patient although its use should be performed with caution due to the potential renal side effects.