Two novel peptides, neuromedin U-8 and U-25, eliciting a potent uterus stimulating activity, have been purified and identified in porcine spinal cord. Sequence analyses and syntheses revealed that neuromedin U-8 is a novel octapeptide with a C-terminal amide structure, while U-25 contains the U-8 sequence at its C-terminus, preceded by paired Arg residues, implicating their biosynthetic relationship. Their potent uterus stimulating activity and hypertensive effect, as well as their unique C-terminal amide structure are indicative of their specialized physiological function. In addition, by utilizing a specific radioimmunoassay for neuromedin B that is a bombesin-like peptide identified in porcine spinal cord, we have isolated two novel "big" neuromedin B, designated neuromedin B-32 and B-30, from pig brain and spinal cord, indicative of their biosynthetic relationship. Nine neuromedins (B, B-30, B-32, C, K, L, N, U-8 and U-25) thus far identified in porcine spinal cord as the smooth-muscle stimulating peptides, are classified into four families; B-(bombesin-like), K-(kassinine-like), N-(neurotensin-like) and U-groups.