The organotellurium compound, trichloro(dioxoethylene-O,O′) tellurate (AS101) has been shown previously to exert diverse biologic activities both in vitro and in vivo. This compound was recently found to react with thiols and to catalyze their oxidation. This property of AS101 raises the possibility that it may serve as a cysteine protease inhibitor. In the present study, using a substrate-specific enzymatic assay, we show that treatment of caspase-1 (interleukin-1β [IL-1β] converting enzyme [ICE]) with AS101 inhibits its enzymatic activity in a dose-dependent manner. Moreover, the results show that AS101 treatment causes a significant reduction in the active form of IL-18 and IL-1β in peripheral blood mononuclear cells (PBMC) and in human HaCat keratinocytes. We further demonstrate that the inhibitory effect of AS101 does not involve nitric oxide (NO) or interferon-γ (IFN-γ), two possible regulators of IL-18 production, and does not occur at the mRNA level, suggesting a posttranscriptional mechanism of action. More importantly, AS101 downregulates IL-18 and IL-1β serum levels in a mouse model of lipopolysaccharide (LPS)-induced sepsis, resulting in increased survival. Recent studies emphasize the pathophysiologic role of IL-18 and IL-1β in a variety of inflammatory diseases. Thus, their blockage by the nontoxic compound, AS101, currently used in clinical studies, may provide clinical advantage in the treatment of these diseases.