Nine children aged 18 months to 17 years (mean 5.7 years) with chronic hepatitis b virus infection and chronic active hepatitis were treated with 5 to 6 million units/m2 of body surface area of interferon -alpha 2b administered subcutaneously three times per week for 4 months (n = 1) or 6 months (n = 8). At 12 months after the start of therapy, six children less than 3 years of age responded to the treatment (three completely and three partially), whereas only one of three children older than 7 years of age responded. We conclude that IFN treatment may be effective in children with chronic HBV infection, especially when administered while they are young.