A neuropeptide hormone isolated from corpora cardiaca of Melanoplus sanguinipes was purified by HPLC. The HPLC fractions were examined for adipokinetic activity with an in vivo bioassay. A single large UV absorbent peak was active in the mobilization of lipid while the other HPLC fractions showed no detectable activity. This large peak had a retention time and amino acid composition identical to synthetic Lom-AKH-I which was analyzed in a parallel manner. The primary sequence structure, pGlu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2, was determined by automated gas-phase Edman degradation. The peptide was deblocked prior to sequencing using pyroglutamate aminopeptidase and the sequence was confirmed with mass spectrometry. The C-terminus of the peptide was determined to be blocked, as indicated by the lack of digestion with carboxypeptidase A. The knowledge of the primary sequence of Mes-AKH allows the use of a commercially available synthetic peptide and its antibodies for use in future research with Melanoplus sanguinipes.