The treatment of HBeAg-negative chronic hepatitis B with alpha interferon alone is unsatisfactory. We evaluated the efficacy of combined administration of interferon-a2a (IFN) with oral ganciclovir, a nucleoside analogue. Forty patients with hepatitis B virus (HBV)-DNA-positive/HBeAg-negative chronic hepatitis B, were randomized to receive 4.5 MU IFN thrice weekly, subcutaneously, alone or in combination with 3 g ganciclovir per os daily for 26 weeks and followed for 12 months after treatment. Mean serum HBV-DNA levels decreased by 4.0 log10 in the combination group (from 5 × 106 to 4.8 × 102 copies/ml) and by 2.2 log10 in the interferon group (from 8 × 106 to 4.8 × 104 copies/ml) by quantitative polymerase chain reaction (PCR). HBV-DNA became undetectable in 11 of 20 (55%) and in three of 20 (15%) patients in the two groups, respectively (P=0.02). The alanine aminotransferase levels became normal in all patients receiving combination therapy, compared to 75% of those in the interferon group. After cessation of therapy, HBV-DNA increased or reappeared in all patients with 85% also relapsing biochemically. One year after treatment, three patients in each group (15%) remained in sustained biochemical remission with very low serum HBV-DNA levels (median 15 700 copies/ml). We conclude that, in HBeAg-negative chronic hepatitis B, 6-month combination therapy with oral ganciclovir and IFN is associated with complete biochemical remission in all treated patients and a 4 log10 decrease in serum HBV-DNA levels. The end of treatment efficacy of this combination scheme is far super- ior to that of IFN monotherapy but sustained responses are few. Further studies are warranted to evaluate the efficacy of prolonged combination schemes with nucleoside analogues and IFN, compared to IFN monotherapy.