LIGHT [homologous to lymphotoxins, shows inducible expression, and competes with herpes simplex virus glycoprotein D for herpes virus entry mediator (HVEM/TR2)] is a new member of TNF superfamily. The HT-29 colon cancer cell line is the most sensitive to LIGHT-induced, IFNγ-mediated apoptosis among the cell lines we have examined so far. Besides downregulation of Bcl-X_L, upregulation of Bak, and activation of both PARP [poly (ADP-ribose) polymerase] and DFF45 (DNA fragmentation factor), LIGHT-induced, IFNγ-mediated apoptosis of HT-29 cells involves extensive caspase activation. Caspase-8 and caspase-9 activation, as shown by their cleavages appeared as early as 24 h after treatment, whereas caspase-3 and caspase-7 activation, as shown by their cleavages occurred after 72 h of LIGHT treatment. Caspase-3 inhibitor Z-DEVD-FMK (benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone) and a broad range caspase inhibitor Z-VAD-FMK (benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone) were able to block LIGHT-ind LIGHT [homologous to lymphotoxins, shows inducible expression, and competes with herpes simplex virus glycoprotein D for herpes virus entry mediator (HVEM / TR2)] is a new member of TNF superfamily. The HT-29 colon cancer cell line is the most sensitive to LIGHT-induced, IFNγ-mediated apoptosis among the cells lines we have examined so far. Besides downregulation of Bcl-X_L, upregulation of Bak, and activation of both PARP [poly (ADP-ribose) polymerase] and DFF45 (DNA fragmentation factor) , LIGHT-induced, IFNγ-mediated apoptosis of HT-29 cells in extensive caspase activation. Caspase-8 and caspase-9 activation, as shown by their cleavages were as early as 24 h after treatment, while caspase-3 and caspase-7 Activation, as shown by their cleavages occurred after 72 h of LIGHT treatment. Caspase-3 inhibitor Z-DEVD-FMK (benzyloxycarbonyl-Asp-Glu-Val- Asp-fluoromethylketone) and a broad range caspase inhibitor Z- VAD-FMK -Val-Ala-Asp fluoromethylketone) were able to block LIGHT-ind