Synthesis and evaluation of physiopathologic effects of agonistic and antagonistic analogs of growth hormone-releasing hormone (GHRH). We synthesized diverse series of agonists and antagonists of GHRH. In the Miami class of GHRH antagonists, based on the favorable physiological properties of fluorinated peptides, we incorporated pentafluoro-Phe at positions 6 or 10 and Orn at positions 12 and 21 into the structures of our analogs of GH-RH. Among these new GHRH antagonists developed for treatment of various cancers are MIA-602, MIA-606, MIA-609, MIA-690 and others. Preclinical evaluation of these new GHRH antagonists, especially MIA-602 and MIA-690 has been carried out in athymic nude mice bearing xenografts of a wide variety of human cancer lines. New GHRH antagonists of AVR class which are even more potent will also be evaluated in models of prostate cancer, pancreatic, colorectal, gastric, renal, and bladder cancer, brain tumors, lung cancer, melanoma, thyroid cancer and leukemia.