Among those plants with chemical constituents that Lewin (1931) classified as Phantastica and which toda y are referred to as hallucinogens or psychotomimetics (Hofmann, 1959), we might include two species of the small leguminous genus Anadenanthera Spegazzini. This genus, formerly considered as section Niopa of the genus Piptadenia Bentham. is the probable source of the so-called narcotics best known as' Cohoba, Vilca and Yopo. 1 use the word 'narcotic' in the classic sense, to indicate a substance one of whose effects consists of a benumbing activity on the central nervous system .