Eight patients with chronic (mean 52 months) type B hepatitis (chronic active hepatitis and active cirrhosis) and markers of active viral replication (presence of HBeAg and HBV-DNA in serum) were treated with Ara-AMP for 7-12 weeks. The mean follow-up time was 18.3 months. All but one patient responded to treatment. In seven patients, HBeAg and HBV-DNA became negative and developed anti-HBe. One patient lost HBsAg as well as HBeAg and HBV-DNA. HBcAg in liver tissue became undetectable or greatly reduced in the seven patients in whom it was strongly positive. Aminotransferase and immunoglobulin levels reverted to normal in the seven responders and remained normal through the entire follow-up period. A second liver biopsy, performed after completion of therapy, showed improvement in six of eight cases, with disappearance of lobular activity. Two patients treated for 12 weeks developed a severe polyneuropathy lasting for 6 months. A 7-week course of Ara-AMP seems to induce long-lasting inhibition of viral replication, along with an improvement in liver function tests and liver histology, without significant side effects. On the other hand, a 12-week course was associated with the development of a severe and prolonged polyneuropathy.