Interleukin-1 (IL-1) is expressed in the mouse brain after intracerebroventricular injection of lipopolysaccharide (LPS) and is thought to be responsible for many of the behavioral and neuroendocrine changes that occur during inflammation. In this study we show that LPS in the brain also induces expression of interleukin-1 converting enzyme (ICE) and that ICE is important for the characteristic anorectic response of mice to intracerebroventricular LPS. Specifically, mice that were deficient in ICE (ICE^/) resisted the anorexia caused by intracerebroventricular injection of LPS but were sensitive to the anorectic properties of recombinant IL-1. The typical anorectic response seen in wild-type (WT) mice after LPS was restored in ICE^/ mice by intracerebroventricular administration of the ICE analog cathepsin G. Conversely, anorexia induced by intracerebroventricular injection of LPS in WT mice was blocked by prior intracerebroventricular injection of the ICE antagonist YVAD.CMK. Furthermore, in situ hybridization immunohistochemistry revealed intense expression of ICE mRNA in the hippocampus and dorsomedial hypothalamus of WT mice after intracerebroventricular injection of LPS. Thus ICE mRNA is expressed in brain after intracerebroventricular injection of LPS and is important for induction of anorexia, presumably because it generates mature IL-1. These results suggest that preventing generation of mature IL-1 can inhibit anorexia induced by LPS in the brain and, therefore, reveal ICE as a potential target for regulating food intake during brain inflammation.