It has recently been shown that thymosin-α1(T-α1), a synthetic polypeptide of thymic origin, is able to promote disease remission and inhibition of hepatitis B virus (HBV) replication in patients affected by hepatitis B e antigen (HBeAg)-positive chronic active hepatitis. We evaluated the efficacy and safety of T-α1 treatment in patients with hepatitis B e antibody (anti-HBe) and HBV-DNA-positive chronic hepatitis. Thirty-three patients were randomly assigned to receive either T-α1 900 microg/m2 body surface area twice weekly (17 patients) or 5 MU of interferon alfa (IFN-α) three times weekly (16 patients) for 6 months. At baseline, both groups were comparable concerning age, sex, liver histology, and alanine transaminase (ALT) levels. At the end of treatment, complete response (defined as ALT normalization and HBV-DNA loss) occurred in 5 of 17 (29.4%) in the T-α1 group and in 7 of 16 (43.8%) in the IFN-α group (P = not significant). After a follow-up period of 6 months, a complete response was observed in 7 of 17 (41.2%) in the T-α1 group and in 4 of 16 (25%) in the IFN-α group (P = n.s.). Compared with the results observed in a group of 15 patients never treated with IFN-α and followed for 12 months, the rate of complete response was significantly higher in the IFN-α group at the end of therapy (1 of 15 vs. 7 of 16, respectively; P < .05) and in the T-α1 group at the end of follow-up (1 of 15 vs. 7 of 17, respectively; P < .05). Unlike IFN- α, T-α1 was well tolerated by all patients. The only side effect, reported by some, was local discomfort at injection sites. The results of this trial suggest that T-α1 is able to reduce HBV replication in patients affected by anti-HBe-positive chronic hepatitis. Furthermore, compared with IFN-α, T-α1 is better tolerated and seems to induce a gradual and more sustained ALT normalization and HBV-DNA loss. In conclusion, T-α1 appears to be a safe and effective alternative treatment for anti-HBe-positive chronic hepatitis. The benefit of this agent in producing long-term inhibition of HBV replication must be confirmed by future trials.