The use of psychotropic plants among the mestizo population of the northwestern Amazonas has already been the subject of some research. However, the field is far from fully invested. Ayahuasqueros locally known by the name of “vegetalistas” or simply “maestros” have preserved considerable knowledge of plant use and still today contribute substancially to the health care of both rural and urban population. The present paper is based on field work with one particular such practitioner, Don Emilio Andrade Gomez, a 66 year-old shaman who lives in the vicinity of Iquitos (3”5OS 73”15W), northeast Peru. Some of the basic ideas of his cosmovision are presented. Special attention is given to the concept of “doctor” or “plant teacher”, applied to certain plants which are supposed to “teach medicine”, if the appropriate conditions of isolation and diet are observed. Some of these plants are added to the hallucinogen beverage known in the region by the name ayahuasca, made from the stem of Banisteriopsis species, and one or several additives. During the period of isolation the spirits of these plants teach the initiate certain melodies or “icaros” that he will later use when practising his shamanistic activities. During field work in 1981 and 1982 the author collected various specimens of “plant teachers”, part of which have now been identified and are also presented.