To elucidate the role of tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) in chronic hepatitis type C (CH(C], TNF alpha and IL-1 beta released from peripheral blood mononuclear cells were measured in 6 CH(C) patients before and during interferon therapy. During the therapy, TNF-alpha levels were significantly high in two patients whose serum ALT levels turned normal, while IL-1 beta levels did not show significant change. These results suggest that TNF-alpha takes part in improvement of CH(C).