Platelet aggregation is initiated by receptor activation coupled to intracellular signaling leading to activation of integrin alpha (IIb)beta (3). Recent advances in the study of platelet receptors for Collagen, von Willebrand factor, thrombin, and adenosine diphosphate are providing new insights into the mechanisms of platelet aggregation. Curr Opin Hematol 2001, 8:270-276 (C) 2001 Lippincott Williams & Wilkins, Inc.