Granulysin is a cytotoxic granule expressed in cytotoxic T cells and natural killer cells. Although its cytotoxic effect against a number of tumor cell lines has been demonstratedin vitro, recent studies with transgenic mice, and a number of clinical studies, have further established its significance in cancer immunology. Furthermore, granulysin-inducedin vitrochemotaxis and activation of both human and mouse dendritic cells have been reported. Given the results in recent clinical studies, granulysin may offer a useful indicator in the prognosis of cancer. Taken together, an understanding of the mechanism by which granulysin destroys target cells would provide vital information in the development of new therapies for the treatment of this disease.