1. An amidated decapeptide, showing strong inhibitory activity of spontaneous visceral muscle movement was isolated, from head extracts of 42 thousand fleshflies, Neobellieria bullata (Diptera, Sarcophagidae). 2. Amino acid sequencing and verification by peptide synthesis revealed the following primary structure: Thr-Asp-Val-Asp-His-Val-Phe-Leu-Arg-PheNH2. 3. The novel peptide was termed neomyosuppressin or Neb-MS. 4. During the process of consecutive high performance liquid chromatography (HPLC) purifications the biological activity of the samples was monitored using heterologous bioassay system. 5. The threshold level of synthetic Neb-MS was found to be 8.6 +/- 0.5 x 10(-11) M on the Leucophaea hindgut and 3.4 +/- 0.5 x 10(-10) M on the Locusta oviduct bioassay, respectively.