The intensive research of recent years has suggested that the cause of ulcerative colitis (UC) involves a genetic predisposition to an uncontrolled or unbalanced immune response to luminal or epithelial antigens or against other external factors. Intercellular adhesion molecule-1 (ICAM-1) is pivotal for the influx of neutrophil granulocytes into colonic mucosa, and gene analyses have found polymorphisms in the gene encoding ICAM-1, indicating that changes in ICAM-1 function may be involved in the pathogenesis of UC. Clinical trials of the ICAM-1 antisense oligonucleotide Alicaforsen, which inhibits the synthesis of ICAM-1, have shown positive results in the treatment of patients with left-sided (distal) UC. In addition to emphasizing the central role of ICAM-1 in active stages of UC, the results provide hope for the development and introduction of a more specific and efficient treatment for UC than those currently available. This review discusses the results from studies on the expression of ICAM-1 in colonic tissue from patients with UC.