“Introduction. the san pedro cactus contains the alkaloid mescaline and other derivates of phenethylamine with hallucinogenic properties. this cactus was used throughout history by a number of different pre-columbine cultures and civilisations that settled in northern peru. in this article we review the ethno-archaeological and ethno-historical evidence of the ritual use of the san pedro cactus in the pre-columbine cultures, and these findings are compared with the information provided by current ethnographical studies. development. the longer a cactus has been stored, the stronger and the higher its content in mescaline-derived alkaloids will be. archaeological evidence has been found of the use of san pedro for magical-religious purposes in the following pre-columbine cultures: cupisnique (1500 bc), chavín (1000 bc), moche (100-750 ad) and lambayeque (750-1350 ad). today’s master shamans use san pedro on altars (‘mesas’) erected for healing rites in order to treat enchantment and bad luck. the mesa follows a sophisticated ritual: ‘levantar’ (raise) or sniff tobacco with alcohol, ingest san pedro, pinpoint the diseases, cleanse the evil and ‘florecer’ (flourish) the sick person. the mesa rite is performed in the early hours of tuesdays and fridays, which are sacred days in the andean religions. san pedro is sometimes replaced by an infusion of plants and seeds that contain hallucinogenic components, such as ayahuasca and the ‘mishas’ (brugmansia sp.). conclusions. the ancient tradition of using the san pedro cactus for healing and hallucinogenic purposes has remained part of the culture in andean shamanism up to the present day. © 2006, revista de neurología.”