The effects of xenopsin, a frog skin peptide, on some isolated tissues, rat blood glucose level and vascular permeability were investigated and compared with neurotensin, a hypothalamic peptide. They had a contractile activity on rat stomach strips and guinea pig ileum, and neurotensin is ca. 2 and 4 times more active in the respective tissue than xenopsin. Neurotensin had a positive inotropic action on isolated guinea pig auricle and was 6 times more active than xenopsin and the action of both peptides could not be blocked by propranolol, phentramine mesylate and diphenhydramine. Xenopsin relaxed the rat duodenum with the activity almost equal to that of neurotensin and these response patterns were different from those induced by bradykinin. In hyperglycemic activity on anesthetized rats, neurotensin was several times more active than xenopsin. Xenopsin had a strong ability to increase vascular permeability and its activity was 2 and 20 times more active than neurotensin and bradykinin, respectively. These data indicate that xenopsin has a similar biologically active pattern as neurotensin and generally neurotensin is more active than xenopsin except for vascular permeability.