The mechanisms of migration of neutrophils into the airway lumen are crucial in the development of airway injury of acute bronchiolitis and are mediated by adhesion molecules. In this study, we have attempted to evaluate the role of serum concentrations of the soluble form of intercellular adhesion molecule-1 (sICAM-1) in the disease activity in acute bronchiolitis and in respiratory syncytial virus (RSV) infection. Circulating levels of sICAM-1 in sera from 10 normal control subjects, and from 47 hospitalized acute bronchiolitis patients at admission, and from 25 patients on the day of discharge were determined by use of commercially available enzyme-linked immunosorbent assay kits. The mean serum level of sICAM-1 in bronchiolitis patients was significantly higher than in the 10 healthy control infants (345.8 +/- 99.7 microg/mL vs 237.1 +/- 81.7 microg/mL; p<0.05). However, the mean sICAM-1 concentration was similar between RSV-positive and RSV-negative patients (337.5 +/- 99.6 microg/mL vs 350.9 +/- 101.1 microg/mL; p=0.65). Although the mean clinical severity score of RSV-positive patients was significantly higher than that of RSV-negative patients (5.94 +/- 1.83 vs 3.48 +/- 1.70; p<0.05). The improvement of clinical severity score was not well correlated with the change of sICAM-1 level (r=0.22). This study provides evidence that serum levels of sICAM-1 are increased in acute bronchiolitis and further confirms the role of adhesion molecules involved in the pathogenesis of the disease. However, the serum concentrations of the soluble adhesion molecules could not reliably reflect the clinical severity of the disease.