Novel synthetic Arg-Gly-Asp containing peptides which have high affinity and specificity for their receptors by virtue of restrictions on their stereochemical conformation. Such restrictions can be provided by cyclization, by inclusion into a constraining conformational structure such as a helix, by providing an additional chemical structure such as an amide or an enantiomer of a naturally occurring amino acid, or by other methods. In particular, there are provided cyclic peptides having increased affinity and selectivity for the certain receptors over that of linear, Arg-Gly-Asp-containing synthetic peptides.