Interferons are glycoproteins which exert a potent inhibitory effect on the replication of hepatitis B virus (HBV). Controlled studies of interferon treatment in patients with chronic HBV infection have shown seroconversion rates, from HBeAg positive to anti-HBe positive, 2 to 3 times higher than without treatment. No enhancement of this effect was observed using combinations of interferon with other antiviral substances. The reason for poor therapeutic response to interferon in the majority of patients with chronic hepatitis B may result from its lost virostatic activity against HBV-DNA located in the cell nucleus.