Isolated human platelets were pre-treated with a low dose of ADP, fractalkine (1µg/ml), or a combination of both for various incubation times and surface expression of P-selectin and activated fibrinogen receptor (PAC-1) was analysed by flow cytometry. We found that fractalkine alone does not substantially enhance surface expression of P-selectin or PAC-1. However, in the presence of ADP, fractalkine showed a synergistically induced expression of P-selectin and PAC-1 compared with ADP alone (p<0.05). This effect could be inhibited by an antagonising anti-fractalkine antibody or by pertussis toxin (PTX) suggesting a G-protein coupled signalling mechanism. Further, Fractalkine was found to enhance in vitro platelet aggregation induced by low levels of ADP, where as platelet aggregation could not be initiated by incubation with the chemokine alone. Next we addressed the effect of fractalkine on platelet adhesion under shear conditions using a flow chamber model. Stimulation with fractalkine significantly enhanced platelet adhesion to collagen and fibrinogen but not BSA. Similar to expression of the described surface markers, enhanced adhesion could be prevented by the antagonizing antibody or preincubation of platelets with PTX. In conclusion, fractalkine, a recently discovered membrane-bound chemokine, synergistically to ADP enhances platelet activation, aggregation and adhesion under flow. Because fractalkine is a membrane-bound chemokine found on inflamed endothelium and in atherosclerotic lesions, stimulation of platelets through fractalkine might play an important role in thrombosis and atherosclerosis.