Two novel neuropeptides with neuropeptide F (NPF)-like immunoreactivity have been isolated from brain extracts of the Colorado potato beetle. Purification was achieved primarily by use of reverse phase chromatography including initial C-18 Sep-Pak cartridges and 4 subsequent analytical HPLC columns. Combined data from automated Edman degradation, immunochemical analysis, u.v. absorbance and mass spectrometry led to the elucidation of their full primary structures. The deduced sequences are: Ala-Arg-Gly-Pro-Gln-Leu-Arg-Leu-Arg-Phe-NH2 (ARGPQLRLRFamide) and Ala-Pro-Ser-Leu-Arg-Leu-Arg-Phe-NH2 (APSLRLRFamide). On the basis of their primary structure both peptides can be appended to the invertebrate group of neuropeptide Y (NPY)-like peptides, generally referred to as NPFs. We suggest these peptides to be designated Led-NPF-1 and Led-NPF-2.