Tumor necrosis factor-alpha (TNF-alpha) is critically involved in a wide variety of inflammatory pathologies, such as hepatitis, via the TNF receptor-1 (TNFR1). To develop TNFR1-targeted anti-inflammatory drugs, we have already succeeded in creating a TNFR1-selective antagonistic mutant TNF-alpha (R1antTNF) and shown that R1antTNF efficiently inhibits TNF-alpha/TNFR1-mediated biological activity in vitro. In this study, we examined the therapeutic effect of R1antTNF in acute hepatitis using two independent experimental models, induced by carbon tetrachloride (CCl(4)) or concanavalin A (ConA). In a CCl(4)-induced model, treatment with R1antTNF significantly inhibited elevation in the serum level of ALT (alanine aminotransferase), a marker for liver damage. In a ConA-induced T-cell-mediated hepatitis model, R1antTNF also inhibited the production of serum immune activated markers such as IL-2 and IL-6. These R1antTNF-mediated therapeutic effects were as good as or better than those obtained using conventional anti-TNF-alpha antibody therapy. Our results suggest that R1antTNF may be a clinically useful TNF-alpha antagonist in hepatitis.