Fluorescently labeled polymorphonuclear leukocytes (PMN) were used to measure adhesion to human umbilical vein endothelial cells (EC) cultured in vitro. Stimulation of PMN with phorbol dibutyrate (PDB), TNF, or C5a caused an increase in adhesion followed by a return to prestimulation levels of adhesion of longer times of incubation. Maximal adhesion of PMN to EC occurred rapidly in response to C5a (5 min) and more slowly with TNF or PDB (15 min). PMN stimulated to adhere with C5a detached from EC by 15 min. PMN from CD11/CD18-deficient patients and PMN incubated with anti-CD18 mAbs failed to bind to EC despite maximal stimulation. Anti-CD11a/CD18 and anti-CD11b/CD18 each partially inhibited adhesion, and a combination of these two reagents completely blocked adhesion. The adhesion we measured was therefore completely dependent on CD11/CD18, and CD11a/CD18 and CD11b/CD18 each contributed to adhesion. Stimuli that enhanced adhesion of PMN to EC also enhanced expression of CD11b/CD18 on the cell surface, but the time course of expression correlated poorly with changes in adhesivity. To determine if changes in the expression of CD11b/CD18 are necessary for the changes in adhesivity, we used enucleate cytoplasts that did not increase expression of CD11b/CD18. Cytoplasts showed a normal rise and fall in adhesivity in response to PDB. We conclude that the transient adhesion of stimulated PMN to naive EC is regulated by changes in the nature of existing CD11/CD18 molecules on the PMN surface. Changes in expression of CD11b/CD18 may contribute to enhancement of adhesivity, but a definite role for this phenomenon has yet to be established.