Lymphocytes are present in atherosclerotic lesion. We hypothesise that platelets may facilitate lymphocyte infiltration into the arterial wall. Reconstituted human blood or whole blood was perfused through a collagen-coated parallel-plate flow chamber at different shear rates. Adhered platelets markedly enhanced lymphocyte adhesion that increased lymphocyte deposition from 10 ± 3 cells/mm2 of platelet-depleted blood to 38 ± 11 cells/mm2 of platelet-containing blood at the arterial shear rate of 500 s-1. Platelet-dependent lymphocyte adhesion was inhibited by P-selectin, CD40L, and GPIIb/IIIa-blocking agents, suggesting the involvement of multiple adhesion molecules in this heterotypic interaction. Lymphocyte deposition was more marked among T cells, and seen in both small and large cells. B and natural killer cell adhesion was, however, mainly seen in small cells. Platelet-conjugation facilitated lymphocyte adhesion, as suggested by the selective deposition of platelet-conjugated lymphocytes. In a mouse model of arterial thrombosis, FeCl3-induced thrombus formation markedly enhanced lymphocyte adhesion and infiltration into platelet thrombi, which was abolished by GPIIb/IIIa inhibition. In conclusion, platelets support lymphocyte adhesion under arterial flow conditions, which is selective among T cells and involves multiple adhesion molecules. Our data imply that platelets may facilitate the recruitment of circulating lymphocytes at the arterial injured sites.