Sixty-four heterosexual Italian carriers of HBsAg with chronic HBeAg and hepatitis B virus DNA-positive hepatitis were assigned randomly either to receive human lymphoblastoid interferon (injections of 5 million units per m2 three times per week for 6 months) or to serve as untreated controls. After 18 months of follow-up evaluation, 26 of the 33 treated patients (79%) had cleared hepatitis B virus DNA, 23 (70%) had lost HBeAg and 20 (61%) had seroconverted to anti-HBe. Fifteen of the 31 controls (48%) had cleared hepatitis B virus DNA (p = 0.01), 12 (39%) had lost HBeAg and nine (29%) had seroconverted to anti-HBe (p = 0.002). Eight treated patients but only one control had lost HBsAg and seroconverted to anti-HBs (24% vs. 3%, p = 0.01). Treated patients cleared hepatitis B virus markers after a mean interval of 4 months, compared with 8 months in the controls. All responders to interferon cleared intrahepatic HBcAg, and 50% showed histological improvement. The baseline hepatitis B virus DNA levels and the original histology were not predictive of a response to therapy; women appeared to respond better than men. Lymphoblastoid interferon provides an effective therapy in the heterosexual Italian patient with chronic hepatitis B.