Intermittent interferon (IFN) therapy appears to be effective for patients with e-antigen-negative chronic hepatitis B who exhibit abnormal fluctuations of alanine aminotransferase (ALT) levels and histological evidence of disease progression. To determine the optimal dose of IFN in such patients, we studied the effects of natural IFN-beta in a prospective, randomized, double-blind, controlled trial in 36 patients with e-antigen-negative chronic hepatitis B who repeatedly demonstrated abnormal fluctuations in ALT levels. Thirty-six patients were randomly assigned to three groups, receiving doses of: 0.3 MIU IFN (group 1; n = 12), 1 MIU (group 2; n = 12), or 3 MIU (group 3; n = 12), administered twice per week for 24 weeks. Patients were regarded as responders if ALT levels remained within the normal range and HBV-DNA tested negative for 6 months after the initiation of the therapy. According to this criterion, treatment was effective in 16.7% of the patients (2/12) in group 1, 33.3% (4/12) in group 2, and 75% (9/12) in group 3, the efficacy rate in group 3 being significantly higher than that in the other two groups. However, in 12 of the 15 responders, (80%) ALT levels were frequently elevated again within 3 years of the termination of IFN therapy. Although IFN was effective in controlling the manifestations of hepatitis in terms of e-antigen-negative patients who exhibited abnormal fluctuations in ALT, it appears that continuous treatment with intermittent high-dose IFN is necessary to maintain ALT levels within the normal range.