This invention relates to therapeutic reagents and peptides, radiodiagnostic reagents and peptides, and methods for producing label radiodiagnostic agents. Specifically, the invention relates to linear peptide derivatives and analogs of somatostatin, and embodiments of such peptides radiolabeled with a radioisotope, as well as methods and kits for making, radiolabeling and using such peptides for radiodiagnostic and radiotherapeutic purposes. The invention specifically relates to linear peptide derivatives and analogues of somatostatin radiolabeled with technetium-99m and uses thereof as scintigraphic imaging agents. The invention so specifically relates to liner peptide derivatives and analogues of somatostatin radiolabeled with cytotoxic radioisotopes such as rhenium-186 (.sup.186 Re) and rhenium-188 (.sup.188 Re) for use as radiotherapeutic agents. Methods and kits for making, radiolabeling and using such peptides diagnostically and therapeutically in a mammalian body are also provide.