Some Mexican cacti of the genera Ariocarpus, Mammillaria, Obregonia, Pelecyphora, Solisia and Turbinicarpus have been studied with respect to their alkaloids and ethnobotany. Seven previously known cactus alkaloids were identified. N,N-Dimethyl-4-hydroxy-3-methoxy-phenethylamine was found to occur in Ariocarpus agavoides. In Pelecyphora aselliformis N,Ndimethyl-3-hydroxy-4,5-dimethoxy-phenethylamine was identified as the major alkaloid. The possible relationship between the vernacular names of these plants and their alkaloid content is discussed.