Bradykinin (BK) is an autocrine growth factor for lung and prostate cancers. BK also facilitates tumor extension by increasing tissue permeability and stimulating angiogenesis. Peptide BK antagonists are in development as potential new drugs for lung cancer. Newer nonpeptide BK antagonists have even higher potency against lung cancer, in vitro and in vivo. These compounds have now been applied to the study of prostate cancers, and have been found to be effective. Prostate cancer cell line PC3 is derived from a late-stage, hormone-independent, metastatic tumor; its growth is difficult to inhibit. Our established BK antagonists, while less effective against this line of prostate cancer in xenografts in nude mice than against lung cancer, are active and have led the way to development of new peptide and nonpeptide agents for prostate cancer. In addition to inhibiting cancer cell growth directly, they inhibit angiogenesis mediated by vascular endothelial growth factor, and inhibit increased tissue permeability mediated by membrane metalloproteases in these tumors. This class of compounds offers hope for development of new drugs for refractory prostate cancer.