This report describes the successful use of the ether soluble, ion pairing reagents perfluoropropoinic and perfluorobutyric acid in the preparative and analytical reserved phase HPLC of underivatised peptides. The preparative separation of a 1-g sample of Pyr-His-Gly, the proposed anorexigenic peptide, is described on C18-silica which was packed in a flexible-walled cartridge and subjected to radial compression. The mobile phase consisted of an aqueous solution of perfluorobutyric acid (5 mM) and a flow rate of 100 ml/min was used. The purified peptide was simply isolated by neutralizing and freeze-drying the corresponding peak and then extracting the excess ion pairing reagent with ether. The product was then shown to be homogeneous by analytical HPLC and amino acid analysis. The tripeptide failed to show any effect on food intake, water intake or body weight in female rats. Similarly no effect was noted on the reproductive cycles of the rat.