Cell adhesion molecules (CAM) are essential for the capture and migration of leucocytes. Ulcerative colitis (UC) and Crohn's disease (CD) are characterized by a continuous infiltration of leucocytes into intestinal tissue, and the colonic contents of P-selectin, PECAM-1, ICAM-1, ICAM-2, and ICAM-3 were therefore studied. Concentrations of these cell adhesion molecules were measured by an ELISA technique in sonicated colonic tissue from patients with UC and CD and controls with non-inflammatory disease and compared with the diagnosis and disease activity. P-selectin, PECAM-1, and ICAM-1 concentrations were elevated in UC patients compared with controls (P = 0.034, P = 0.014, P = 0.017, respectively), whereas that of ICAM-2 was not. The concentrations of these CAM did not differ in CD. In contrast, higher concentrations of ICAM-3 were found in the CD patients than in either UC (P = 0.001) or controls (P = 0.004). The CAM concentrations increased with disease activity, although only ICAM- 1 was significantly elevated (P = 0.017). As considerable differences were found between UC and CD with comparable stages of inflammation, the mere presence of inflammation cannot solely explain the results. The observed differences in the CAM concentrations in UC and CD support the hypothesis that UC and CD are two distinct disease entitles with separate pathogenic mechanisms.