Methanol extracts of the fresh skin of Chinese amphibian Bombina orientalis, caused contraction of the smooth muscles of Wistar rats in vitro. The active extracts were isolated twice by column chromatography of alkaline alumina and sephadex G-15, so that the bioactive eluate C-12 was obtained. The bioactivity of C-12 was inactivated by hydrolysis with chymotrypsin, but not antagonized by cyproheptadine. C-12 was further isolated by reverse phase-high performance liquid chromatography (RP-HPLC). The elution time of C-12-b peak corresponded to that of bombesin standard and their bioactive peak was identical as well. The peaks of the two peptides on RP-HPLC graphs were found to overlap each other. Furthermore, it was revealed that both peptides had the same amino acid composition.The above experimental results suggest that C-I2-h peptide is most probably bombesin.