Apoptosis is instrumental in several physiological/pathophysiological processes and is a frequently used end-point in the development of anti-neoplastic compounds. Despite ample data on several colon cancer cell lines, little is known about the susceptibility of human colon to apoptosis following treatment with established chemotherapeutics. By treating fresh human colonic explants with 5-Fluorouracil (200 microg/ml), CPT-11 (100 microg/ml) and/or TRAIL (100 ng/ml) we readily detected a signal in situ using FITC-VAD-FMK at different time points, whereas labeling of colonic explants with EGFP-conjugated Annexin V proved less specific. Although TRAIL treatment alone appeared to cause little apoptosis in human colonic epithelia versus the control, we observed a greater number of cells undergoing apoptosis when a combination of CPT-11 and TRAIL was used as compared to either agent alone. This is the initial demonstration of TRAIL-induced apoptosis with or without a chemotherapeutic agent in fresh primary human colon epithelia explants. Thus, human colonic explants may provide a valuable reference point when candidate therapeutic compounds triggering apoptosis in colon cancer cell lines, xenografts or mouse models are developed. The results support the feasibility of developing non-invasive optical imaging strategies to detect apoptosis through direct visualization of injury to human colonic epithelia in vivo.