Interferon-beta was given weekly for 24 wk, at a dose of 3 million units, intravenously, to 10 patients with chronic hepatitis B who were serologically positive for HBsAg and HBeAg. Their condition was followed for 6 months after the end of therapy. Both serum hepatitis B virus-associated DNA-polymerase activity and alanine aminotransferase level became significantly lower during therapy and during the 6 months after the end of therapy than at the beginning of therapy. In five of 10 patients, the seroconversion from HBeAg positive to anti-HBe positive had occurred by 6 months after the end of therapy, and in four of these five patients, serum alanine aminotransferase level became normal. Weekly interferon-beta administration over 6 months seems effective in inducing seroconversion and in normalizing serum alanine aminotransferase level.