AIM: To investigate the effects of exogenous melatonin on bacterial translocation and apoptosis in a rat ulcerati-ve colitis model. METHODS: Rats were randomly assigned to three groups: groupⅠ: control, group Ⅱ: experimental colitis, group Ⅲ: colitis plus melatonin treatment. On d 11 after colitis, plasma tumor necrosis factor-α, portal blood endotoxin levels, colon tissue myeloperoxidase and caspase-3 activity were measured. Bacterial translocation was quantified by blood, lymph node, liver and spleen culture. RESULTS: We observed a significantly reduced inciden-ce of bacterial translocation to the liver, spleen, mesen-teric lymph nodes, portal and systemic blood in animals treated with melatonin. Treatment with melatonin signifi-cantly decreased the caspase-3 activity in colonic tissues compared to that in trinitrobenzene sulphonic acid-trea-ted rats (16.11 ± 2.46 vs 32.97 ± 3.91, P < 0.01). CONCLUSION: Melatonin has a protective effect on ba-cterial translocation and apoptosis. AIM: To investigate the effects of exogenous melatonin on bacterial translocation and apoptosis in a rat ulcerati-ve colitis model. METHODS: Rats were randomly assigned to three groups: group I: control, group II: experimental colitis, group III: colitis plus melatonin treatment . On d 11 after colitis, plasma tumor necrosis factor-α, portal blood endotoxin levels, colon tissue myeloperoxidase and caspase-3 activity were measured. Bacterial translocation was quantified by blood, lymph node, liver and spleen culture. significantly reduced inciden-ce of bacterial translocation to the liver, spleen, mesen-teric lymph nodes, portal and systemic blood in animals treated with melatonin. Treatment with melatonin signifi-cantly decreased the caspase-3 activity in colonic tissues compared to that in trinitrobenzene sulphonic acid-trea-ted rats (16.11 ± 2.46 vs 32.97 ± 3.91, P <0.01). CONCLUSION: Melatonin has a protective effect on ba-cterial translocation and apopto sis.