A recombinant human TNF receptor Fc fusion protein (rhuTNFR:Fc) was assessed for antiarthritic activity using murine type II collagen-induced arthritis in mice. DBA/1 mice were immunized with bovine type II collagen and treated with rhuTNFR:Fc either from day 21 to day 28 (preventative protocol), or after disease onset for fourteen days (therapeutic protocol). Control mice received either sterile saline or human serum albumin injections. rhuT-NFR:Fc treatment significantly reduced both the incidence and the severity of collagen-induced arthritis in the preventative protocol. Mice receiving rhuTNFR:Fc therapeutically progressed to less severe disease than did control animals, and the arthritis index in rhuTNFR:Fc treated mice was significantly lower than the index in control mice from 7.5 weeks after treatment. The antibody response to collagen was significantly reduced by treatment with rhuTNFR:Fc in both the preventative and therapeutic protocols. No difference was observed in the proliferative response to type II collagen or Con A, but the response to LPS was significantly lower in rhuTNFR:Fc treated mice at the conclusion of both the preventative and therapeutic trials. The results suggest that rhuTNFR:Fc may have both immunosuppressive and antiarthritic properties in this experimental model, and may represent a useful approach to the treatment of autoimmune arthritis.