Abstract: The tripeptide sequence Arg-Gly-Asp (RGD) has been shown to inhibit the adhesive and aggregatory functions of platelets by binding to platelet receptor GP IIb/IIIa. Fibrinogen binding to GP IIb/IIIa represents the final common event that leads to platelet aggregation regardless of platelet activation and, in certain circumstances, is the primary cause of a variety of human cerebral and cardiovascular diseases[1]. The knowledge of the preferred conformation of the RGD sequence together with structure-activity relationship (SAR) analyses should lead to a better understanding of the characteristics important for high affinity binding to GP IIb/IIIa.