The alphaIIbbeta3 receptor, which is the most abundant receptor on the surface of platelets, can interact with a variety of adhesive proteins including fibrinogen, fibronectin and the von Willebrand factor. Fibrinogen binding on alphaIIbbeta3 is an event essential for platelet aggregation and thrombus formation. Mapping of the fibrinogen-binding domains on alphaIIb subunit suggested the sequence 313-332 as a possible binding site. This region was restricted to sequence alphaIIb 313-320 (Y313MESRADR320) using synthetic octapeptides overlapping by six residues. The YMESRADR octapeptide inhibits ADP-stimulated human platelets aggregation and binds to immobilized fibrinogen. In this study, we used the Ala scanning methodology within the sequence 313-320 aiming to evaluate the contribution of each amino acid in inhibiting platelet aggregation. It was found that the substitution of Y313, M314, E315 or S316 by A does not affect the activity of the parent octapeptide. The-RADR-motif seems to be the most essential for the biological activity of the alphaIIb 313-320 site. The conformational analysis of the YAESRADR, YMESAADR and YMESRAAR analogs by using NMR spectroscopy and distance geometry calculations revealed significant differences in their conformational states in DMSO-d6.