Abstract: Integrin α_vβ₃ is highly expressed on activated endothelial cells during angiogenesis and sollid tumor cells. It has been shown to play an essential role in the regulation of tumor growth, local invasiveness, metastatic potential, especially in angiogenesis. Radiolabeld peptides including the tripeptide sequence arginine-glycine-aspartic acid (single-letter code RGD), which can bind to the α_vβ₃ integrin with high affinity and selectivity, have been developed for determination of α_vβ₃ integrin expression.