The involvement of glycoprotein (GP) IV (CD36) in arachidonic acid uptake by human platelets was investigated using an anti-CD36 monoclonal antibody (MAB). The binding of [14C]arachidonic acid to MAB-treated platelets was significantly reduced compared with untreated platelets. The MAB also inhibited arachidonic acid-induced platelet aggregation and thromboxane A2synthesis in a dose-dependent manner. Pre-incubation of gel-filtered platelets with the MAB (10mg/I) inhibited arachidonic acid-induced platelet aggregation by 50% and collagen-induced platelet aggregation by 7-8% and the lag time was increased by 200%. Although the mechanism of platelet aggregation is not fully understood yet, the inhibition of arachidonic acid-induced platelet aggregation by the MAB could be the result of a reduced uptake of exogeneously added arachidonic acid by the MAB-treated platelets. Our data clearly indicate that arachidonic acid uptake by platelets is mediated, at least in part, by CD36.