HUVEC and THP-1 treatment with sialidase abolished the platelet-mediated (ratio 3:1) augmentation of rolling and subsequent adhesion of THP-1 cells at 400 s⁻¹. Sialidase treatment of platelets had no effect. Combined sialidase digestion of HUVEC and platelets did not further reduce THP-1/endothelial cell interaction in the presence of activated platelets (n = 4, *P < .05).