A novel anti-inflammatory drug, IS-741, blocked the adhesion of inflammatory cells to microvascular endothelial cells in vivo and in vitro. We examined the efficacy of IS-741 in a dextran sulfate sodium (DSS)-induced colitis model. DSS colitis was induced by the oral administration of 3% DSS for 10 days in rats. The rats were then divided in two groups: a 1% DSS plus IS-741 group and a 1% DSS plus water group. IS-741 was dissolved in water and administered orally (10 mg/kg) once per day for 14 days. The rats treated with DSS plus IS-741 remained healthy, and their body weight increased. The wet weight of the colon was significantly lower and the total colon length was significantly longer in the IS-741-treated group. Histological examinations revealed a marked infiltration of inflammatory cells into both the mucosa and submucosa in the DSS plus water group, but these changes were attenuated in the IS-741-treated group. The mucosal damage score was significantly reduced by treatment with IS-741. IS-741 also significantly reduced the mucosal myeloperoxidase activity. FACS analysis revealed that IS-741 significantly reduced Mac-1 expression on blood neutrophils. In conclusion, IS-741 suppressed DSS-induced experimental colitis in rats. Some of the action of IS-741 may be associated with its inhibitory effects on the Mac-1 expression of neutrophils in association with the blockade of their adhesion to endothelial cells. The findings in this study suggest that IS-741 may be a useful new therapeutic agent for inflammatory bowel disease.