Neutrophil adherence to endothelial monolayers in multi-well plates can be rapidly quantitated, using a fluorescent plate reader. The number of adherent neutrophils which have been labeled with biscarboxyethyl carboxyfluorescein (BCECF) was calculated by comparing fluorescence of endothelial monolayers to a reference standard curve determined by fluorescence intensity of suspensions of labeled neutrophils. The limit of sensitivity approached 100 cells, which is similar to that achieved by the most sensitive of alternate techniques. The assay, after isolation of the neutrophils, can be completed in 1.5 h. The ability to utilize microwell plates permits the use of large numbers of samples. This method has the advantage of being relatively simple and rapid while maintaining a sensitivity comparable to alternate approaches which employ radioactive labeling or counting of adherent or non-adherent cells.