A novel neuropeptide acting as a myosuppressor on esophagus, funnel and mantle muscular fibers has been isolated from the stellar ganglia of the mollusk cephalopod Sepia officinalis by means of HPLC analysis. Fractions were monitored using a myotropic bioassay. After three separation steps, MALDI-TOF spectrum revealed one main peak at m/z 756.6. The partial N-terminal and C-terminal digestions by exopeptidases followed by MALDI-TOF analysis allowed the determination of the nature of the two C-terminal and N-terminal amino acids. Post Source Decay fragmentation of the molecular ion accurately determined the following primary sequence: Val-Tyr-Ser-Ala-Pro-Tyr-Gly-OH. The mapping of this heptapeptide performed in ESI-MS revealed that its distribution is restricted to the stellar ganglia, the giant fibers III, and the nervous bundle containing the giant fibers II and the palleal nerve. The neuropeptide was not detected in the hemolymph suggesting a release by nerve endings next to the targets.