SummaryA newly developed ELISA was used to detect and quantify the presence of a soluble form of intercellular adhesion molecule‐1 (sICAM‐1) in the circulation of healthy individuals compared with patients with psoriasis vulgaris. Seventeen psoriatic patients were studied. The extent of skin lesions was rated by the psoriasis area and severity index (PASI). Seventeen age‐ and sex‐matched healthy individuals served as controls. Serum levels were measured by an ELISA technique utilizing an anti‐ICAM‐1 murine monoclonal antibody bound to the solid phase, and a second, peroxidase‐conjugated monoclonal antibody reacting with sICAM‐1. Serum levels in controls were 358.8±87.9 ng/ml sICAM‐1, and 480.5±133.6 ng/ml in psoriatics (mean±SD;P=0.02). In psoriasis. sICAM‐1 levels were found to be directly proportional to the PASI score (y=363.002 + 8.525x,R=0.55.P=0.021). These data suggest that the concentration of sICAM‐1 in serum increases during psoriatic inflammation. The origin and function of sICAM‐1 in psor