Platelet endothelial aggregation receptor 1 (PEAR1) is a platelet receptor that signals upon the formation of platelet-platelet contacts independent of platelet activation and secondary to platelet aggregation. Upon platelet aggregation stimulated by physiological agonists, PEAR1 becomes tyrosine- and serine-phosphorylated; the tyrosine phosphorylation can be inhibited by eptifibatide, an aIIbbeta3 antagonist that also inhibits platelet aggregation. Recent studies have indicated that genetic variations in PEAR1, may be associated with enhanced agonist-induced platelet aggregation.