From a side fraction obtained in our previous isolation of neuromedin B from porcine spinal cord, we have purified another decapeptide that exhibits a potent stimulant effect on the smooth muscle preparation of rat uterus. By microsequencing and synthesis, the amino acid sequence of the peptide has been identified as: Gly-Asn-His-Trp-Ala-Val-Gly-His-Leu-Met-NH2. This peptide is found to be identical with the carboxy-terminal subsequence [18-27] of gastrin releasing peptide, and to display a potent contractile activity on rat uterus in the characteristic manner of bombesin. These facts strongly suggest that the peptide may be a neuromediator in the neural communication systems of mammals. We propose the name "neuromedin C" for this peptide, since it is closely related to "neuromedin B", recently identified as a bombesin-like mammalian peptide.