Murine recombinant soluble intercellular adhesion molecule-1 (sICAM-1) was produced and characterized. When immobilized on plastic microtiter wells, sICAM-1 efficiently mediated LFA-1-dependent cell adhesion, indicating that the purified protein retained the ability to bind to LFA-1. However, sICAM-1 in solution, at concentrations up to 100 micrograms/ml, was incapable of inhibiting the phorbol ester-induced homotypic aggregation of lymphocytes, the adhesion of T cells to plastic immobilized sICAM-1, and CTL effector function, all of which are mediated by intercellular adhesion molecule-1:LFA-1 interaction. In contrast, uniform polystyrene microspheres coated with sICAM-1 bound specifically to LFA-1+ cells and efficiently inhibited the adhesion of T cells to immobilized sICAM-1. The sICAM-1-coated microspheres also inhibited CTL function, but the inhibition was only partial. These results suggest that although monomeric sICAM-1 cannot competitively inhibit cell adhesion mediated by intercellular adhesion molecule-1 and LFA-1, microspheres coated with sICAM-1 can inhibit such cell adhesion.