Seven chronic carriers of hepatitis B virus (HBV) were studied during treatment with interferon-alpha to determine whether tumour necrosis factor alpha (TNF alpha) or interleukin-1 beta (IL-1 beta) contributed to the elimination of HBV. Four patients responded to interferon-alpha with clearance of HBeAg and permanent inhibition of HBV replication within 3-12 weeks; in each of these patients, the changes were accompanied by substantial rises in spontaneous in-vitro production of TNF alpha and IL-1 beta by peripheral blood mononuclear cells from previously undetectable levels. There was little or no change in spontaneous TNF alpha and IL-1 beta production in the three patients who did not lose HBeAg in response to interferon-alpha. These findings suggest that TNF alpha and IL-1 beta may contribute to the permanent elimination during interferon-alpha treatment of hepatocytes supporting viral infection and that the therapeutic potential of these cytokines is worthy of investigation.