Fas ligand is a well-characterized apoptosis inducer. Here we demonstrate that Fas ligand induces the processing and secretion of interleukin-1β (IL-1β) in peritoneal exudate cells. This IL-1β secretion is independent of IL-1β converting enzyme (caspase 1), yet it is inhibited by caspase inhibitors, indicating that a caspase (s) in addition to IL-1β converting enzyme can process IL-1β. Inoculation of tumor cells expressing Fas ligand into wild-type mice induces a massive neutrophil infiltration that is, in contrast, suppressed in IL-1α/β knockout mice. These results demonstrate a newly discovered role for Fas ligand in inflammation, and challenge the dogma that apoptosis does not induce inflammation.