We examined the effects of treatment with rHuTNF on food consumption and body weight in C3H/HeJ mice. rHuTNF was administered intraperitoneally either by injections of 3, 12, or 24 micrograms twice a day or by implantation of osmotic pumps that released 0.75, 3, or 12 micrograms per day. Dose-dependent reductions in both food intake and weight were induced by rHuTNF. However, in spite of continued exposure to rHuTNF, the mice developed a resistance to rHuTNF and resumed their pretreatment food intake and weight. Non-immunological factors may play a role in the development of this tolerance, since it developed rapidly and faded within 2 wk of cessation of exposure to rHuTNF.