Caspases, a family of cysteine proteases, play an important role in programmed cell death. In our study, xanthohumol alone did not cleave the examined caspases (-3, -8, -9). Here we have shown that TRAIL in combination with xanthohumol cleaved caspases-8, -9, and -3 ( Figure 6A-C) after 2 and/or 8 h. In order to confirm that apoptosis induced by TRAIL in combination with xanthohumol is dependent on caspases, we used caspase inhibitors: caspase-3 inhibitor (iC-3, z-DEVD-fmk), caspase-8 inhibitor (iC-8, z-IETD-fmk), caspase-9 inhibitor (iC-9, z-LEHD-fmk), and pancaspase inhibitor (iVAD, z-VAD-fmk). The use of caspase inhibitors in combination with TRAIL and xanthohumol caused a significant inhibition of apoptosis in LNCaP cells from 73.9˘0.7 to 11.5˘0.6 with iC-3, 11.2˘0.6 with iC-8, 13.7˘0.6 with iC-9, and 13.9˘0.9 with iVAD ( Figure 7). These results suggest that TRAIL-induced apoptosis in combination with xanthohumol extends extrinsic pathway involving caspases.   The results are expressed as means ± SD obtained from three independent experiments. The β-actin was used as a control to show equal loading of proteins. The **data** were normalized to the control and β-actin level. A statistical significance of the differences between the treatment and control results is marked with * p < 0.05, ** p < 0.01, *** p < 0.001.