In a field screening of Mexican cacti for the presence of alkaloids, Echinocereus cinerascens (DC.) Riimpler and Pilosocereus chrysacanthus (Web.) Byl. et Rowl. were found to give positive tests with the Dragendorff reagent [1]. Plants were collected and the alkaloids extracted and studied. The present report describes the isolation and identification of the major phenethylamine alkaloids of these two cactus species. Although several alkaloid screening papers have listed various Echinocereus species [2-4], only one species, E. merkeri, has been investigated in more detail. N,N-dimethyl-3,4-dimethoxyphenethylamine was isolated for the first time from E. merkeri, which contains several additional phenethylamines and the tetrahydroisoquinoline salsoline [5, 6]. We have now identified the major alkaloid of E. cinerascens as N,N-dimethyl-3,4-dimethoxyphenethylamine. Alkaloid extraction followed by fractionation on an alumina column led to the isolation of this compound, as well as small amounts of N-methyl-3,4-dimethoxyphenethylamine. E. cinerascens has an edible fruit [7] and dry plants are used as fuel [8], but no medicinal uses seem to have been recorded for E. cinerascens or Pilosocereus chrysacanthus. The major alkaloid of the latter species was identified as N-methyl-3,4-dimethoxyphenethylamine. The alkaloids now isolated were identified by comparison with synthetic reference materials using TLC, GC, IR, and MS. A part of the N,N-dimethyl-3,4-dimethoxyphenethylamine isolated from E. cinerascens was oxidized to the corresponding 3,4-dimethoxybenzoic acid, identified by IR and mp comparison with an authentic sample. N-Methyl- and N,N-dimethyl-3,4-dimethoxyphenethylamine have been reported from E. merkeri [5], and are also found in other genera of the Cactaceae, e.g. Coryphantha [9] and Ariocarpus [10].