Background: A soluble form of intercellular adhesion molecule-1 (sICAM-1) shed from endothelial cells is present in the circulation. Whether the circulating molecules represent passive turnover of surface ICAM-1 or may have some active functions in the inflammatory process is unknown. Glucocorticoids (e.g. prednisolone) are cornerstones in the treatment of acute exacerbations of ulcerative colitis (UC), and influence of the leucocyte/endothelial interaction appears to be part of their mode of action. The aim of the present study was therefore to evaluate the ICAM-1-shedding through measurements of sICAM-1 concentrations during prednisolone treatment of UC patients. Methods: Prednisolone (40 mg) was prescribed to 15 patients with severe disease activity. At inclusion, and after 2 weeks of treatment, plasma sICAM-1 levels were measured using the ELISA technique. Results: The concentrations of sICAM-1 were significantly decreased during treatment from median 256.2 (ng/ml) (interquartile range 239.7-321.0 ng/ml) to 220.4 ng/ml (196.0-276.3 ng/ml) (P < 0.01). This reduction correlated with a decrease in disease activity (r_s = 0.8; P < 0.003). Conclusions: sICAM-1 seems to be a poor diagnostic tool, but since plasma sICAM-1 concentrations decreased during the treatment period, it might prove to be applicable as an activity marker in the individual patient.