A 36 amino acid residue peptide, which contains a substance K sequence at its C-terminus has been isolated from porcine brain extracts. The primary structure of the peptide, designated neuropeptide K (NPK), was found to be: (sequence; see text) This N-terminally extended form of substance K is present in a high concentration in the brain. The peptide is highly biologically active with regard to gallbladder contraction, protein extravasation, hypotension and bronchial smooth muscle spasm and may act as an additional tachykinin neuromessenger.