There is a family of proteins - integrins, which are generally expressed at low levels on epithelial cells and mature endothelial cells, but they are highly expressed on the surface of both endothelial cells in tumor neovasculature and some tumor cells, including osteosarcomas, neuroblastomas, glioblastomas, melanomas, and carcinomas of the lung, the breast, the prostate, and the bladder. The alpha(v)beta(3) integrin plays a critical role in angiogenesis and tumor metastasis. Angiogenic blood vessels overexpress alpha(v)beta(3) integrin, as in tumor neovascularization, while alpha(v)beta(3) integrin expression in other microvascular beds and organs is limited. Therefore, alpha(v)beta(3) integrin is a suitable receptor for tumor-targeting therapy and imaging. The alpha(v)beta(3) integrin-targeting properties and the therapeutic potential of various radiolabeled RGD peptides are herein discussed.