Granulysin is a cytotoxic granular protein that was identified from human T cells by using the gene subtraction method in 1987. Based on its amino acid homology, granulysin belongs to the saposin-like protein family. The bioactive 9-k Da form of granulysin is processed from the 15-k Da pro-product in the cytoplasmic granules. It is expressed in CD8-positive αβT cells 5 d after mitogenic stimulation and constitutively in natural killer(NK) cells and γδT cells, although regulation of its expression has not yet been precisely determined. The 9-k Da granulysin form has anti-microbial activity against microorganisms such as bacteria, fungi, mycobacteria and parasites, as well as tumoricidal activity against some tumors at 1-10 μmol/L concentrations. Granulysin is secreted in both Ca-dependent and-inde-pendent manners. In sera, only the 15-k Da form is detectable and is expected to be a biomarker for immune potency, acute viral infection, anti-tumor immune reaction, acute graft vs host disease, and NK cell associated neoplasm. Granulysin is a cytotoxic granular protein that was identified from human T cells by using the gene subtraction method in 1987. Based on its amino acid homology, granulysin belongs to the saposin-like protein family. The bioactive 9-k Da form of granulysin is processed from the 15-k Da pro-product in the cytoplasmic granules. It is expressed in CD8-positive αβ T cells 5 d after mitogenic stimulation and constitutively in natural killer (NK) cells and γδ T cells, although regulation of its expression has not yet been Preciously determined. The 9-k Da granulysin form has anti-microbial activity against microorganisms such as bacteria, fungi, mycobacteria and parasites, as well as tumorigenic activity against some tumors at 1-10 μmol / L concentrations. Granulysin is secreted in both Ca In sera, only the 15-k Da form is detectable and is expected to be biomarker for immune potency, acute viral infection, anti-tumor immune reaction, acute graft vs host disease, and NK cell associated neoplasm.