In this study, immunohistochemistry was used to examine the changes in the density of colonic endocrine cells - argyrophil and argentaffin cells, chromogranin A (CGA), serotonin, somatostatin and glucagon-containing cells in trinitrobenzene sulfonic acid (TNBS)-induced rat colitis. Ulcerative colitis was induced by the instillation of 10 mg of TNBS into the colonic lumen through the anus. To confirm the inducement of ulcerative colitis, the macroscopic and microscopic scores as well as the colonic myeloperoxidase (MPO) activities were monitored for 8 days after TNBS instillation in the colonic lumens. In addition, the number of argyrophil and argentaffin cells, CGA, serotonin, somatostatin and glucagon-immunoreactive cells were counted in the colonic mucosa, respectively. After TNBS instillation into the lumen of the colon from the anus in rats, increases in macroscopic and microscopic scores in the colon tissues were observed along with increases in the colonic MPO activities. Therefore, ulcerative colitis was relatively well induced by the TNBS instillations. Marked decreases in the number of colonic endocrine cells were detected in the TNBS-treated animal compared to the sham control. These results suggest that colonic endocrine cells were also disrupted by TNBS-induced ulcerative colitis.