Endothelial cells respond to several cytokines by a rapid increase in expression of the adhesion molecules E-selectin and intercellular adhesion molecule-1 (ICAM-1), followed by a gradual decline. The fate of these molecules, which was so far unknown, was studied. Specific sandwich ELISA for the detection of soluble (s)E-selectin and sICAM-1 were developed. In supernatant, centrifuged 3 hr at 100,000 g to remove microparticles, from human umbilical vein endothelial cells (HUVEC) activated with tumour necrosis factor (TNF), interleukin-1 (IL-1) or lipopolysaccharide (LPS), E-selectin and ICAM-1 molecules could be detected. Biochemical analysis revealed that sE-selectin migrated as a band of approximately 94,000 MW. The amount of soluble adhesion molecules released was directly correlated with cell surface expression. Maximal release of E-selectin was observed 6-12 hr after activation of HUVEC and decreased to below detection limit 24 hr after activation. After activation, release of ICAM-1 gradually increased with ICAM-1 cell surface expression, and reached a plateau after 24 hr, which was constant for 3 days. Since E-selectin and ICAM-1 are highly expressed at inflammatory sites, the resulting high concentrations of released E-selectin and ICAM-1 may affect interactions of leucocytes with endothelial cells. The physiological role, however, of the release of E-selectin and ICAM-1 remains to be elucidated.