Twenty-four children with chronic active hepatitis due to hepatitis B virus (HBV) infection, who were positive for HBeAg and had increased levels of transaminases, were included in a controlled study of treatment using recombinant interferon-alpha (rIFN-alpha), 10 MU/m2 body surface, intramuscularly, 3 times a week over a period of 3 months. During therapy, a significant decrease in HBV-DNAp was observed in the 12 patients treated. By the end of therapy, the HBV-DNA had disappeared in 3 children, the same occurring in 1 child (33% overall) during the course of the 4th month. By this time, all the controls remained with HBV replication markers (p less than 0.05). The 4 treated patients who responded became HBeAg-negative, developing anti-HBe during the first 12 months after therapy. In the control group, the HBV-DNA disappeared in 3 children in the 7th month of follow-up. All of the children remained HBsAg-positive. The therapy with rIFN-alpha was well tolerated, secondary effects consisting of a flu-like syndrome and a slight decrease in leukocytes and platelets. At the second biopsy, 15 months after the beginning of therapy, a significant decrease in Knodell's index of histological activity was observed in the responders. In the light of these results and since treated children lost viral replication markers in a shorter period of time than the controls, who seroconverted spontaneously, we consider that rIFN-alpha may be useful in the treatment of chronic hepatitis B in childhood.