A high-performance liquid chromatographic procedure with photodiode-array detection has been developed to create phytochemical profiles of phenylalkylamine-containing cactus species. The basic methanolic cactus extracts with methoxamine as internal standard were separated on a 3-μm ODS column with acetonitrile-water-phosphoric acid-hexylamine as the mobile phase. Peak assignation was performed by on-line UV detection (190-300 nm) and by gas chromatography-mass spectrometry of the isolated compounds. The quantitation of mescaline was done at 205 nm. The excellent sensitivity (the detection limit of mescaline was 500 pg, corresponding to 0.002% in cactus material) allowed the analysis of milligram amounts of cactus material taken from living plants. The mescaline content of the psychotropic Peyote cactus Lophophora williamsii (Lem. ex Salm-Dyck) Coult. ranged from 680 to 1010 mg per 100 g. The morphologically very similar Lophophora diffusa (Croizat) Bravo could be differentiated by the absence of mescaline and the dominant alkaloid pellotine. © 1992.