1. For the first time in Peru, a study of the "ayahuasca" is carried out which includes folkloric, botanical and pharmacognostic aspects correlated to it, as well as an experimental test of the pharmacodynamic and toxicological action of its active substance, after recognition of its chemical identity and of one of its plant sources obtained in the Ucayali region. Such a study is the preliminary part of a research oriented in the field of experimental psychiatry today. 2. The methodological aspect indicates — apart from information on the conditions and methods of study itself — the procedure followed to ensure success in obtaining the material and to certify the positive data of the subsidiary to pharmacopsychiatric experimentation and other implications arising from the medical study of the subject. The main checks carried out in this regard are: a) The plant species from Contamana (Loreto Department) is identified as the Cabi paraensis Ducke, whose existence in the Peruvian jungle was not previously known. b) Two effective methods for extracting the active substance from which a quantity is provided that will broadly ensure the feasibility of further pilot tests. c) It is recognized as harmine — alkaloid first extracted from the Harmala Peganum — using chemical, chromatographic and spectrophotometric methods. (These research were conducted at the Department of Botany and Phytochemistry of the Faculty of Pharmacy at the National Major University of San Marcos). 3. The relevant folkloric data are given in detail together with the contribution of personal observations. The following points can be cited as the main conclusions: a) The consumption of the psychoactive potion, whose vulgar name "ayahuasca" in Peru and Ecuador, "capí" in Brazil and Venezuela and "yajé" in Colombia, is widely spread to the Aboriginal people of the Amazon forest since time immemorial. b) Its most frequent uses are related to the practices of curative sortileges, magical communication, "thelepathic" linkage, divination and prediction, which are specific to the animist interpretation of the world at primitive cultural levels. It is also worth emphasizing its use in the production of states of euphoria " paradisiac" which among the wild is reserved for expansive ceremonials and which is spreading to some sectors of civilian populations close to those. c) The area of consumption in Peru apparently includes all jungle regions east of the Andes Mountain, being larger in the North East. 4. Following the stories of self-experiences conducted by various researchers and the communication of two recent medical research, it can be concluded with certainty, in the possibility of inducing psychopathological phenomena with the production of pseudoperceptions mainly visual accompanied by intense motor and neurovegetative reactions, whether isolated harmine or potion is used. However, the nature of the hallucinations induced in relation to the state of consciousness in which they occur, it was suggested that it might correspond to that of the hypnagogic "imaginary". 5. By reviewing the literature for plant species used as sources for breeding, it can be established, with certainty, that all belong to the Malpighiaceae family, being the Cabi paraensis Ducke, the Banisteria caapi Spruce, the Banisteria quitensis (Ndz) Morton, the Banisteria inebrians Morton and possibly also the Banisteria Metallicolor Juss, muricata or Argentee. It is also established that all references about Haemaddicyon amazonicum toxicity have been based on erroneous assessments. 6. With regard to the harmine, its most important chemical nature and properties are identified and a historic review of the pharmacognostic research that recognized it in the Malpighiaceae family. On recognition we can conclude that, experimentally, it occurs for the first time in 1928, in the Banisteria caapi Spruce; in 1953, in the Banisteria inebrians Morton and in 1959, in the Cabi paraensis Ducke. Similarly, it can be assured that all the species mentioned do not contain another alkaloid in addition to the harmine. 7. In the experimental part, two series of tests are conducted to determine the pharmacodynamic and toxicological action of the harmine. The first is aimed at characterizing somatomotor and neurovegetative responses by studying intoxication and the second, at recording changes in blood pressure and breathing in anesthetized animals and with kinographic records. The results are detailed on both aspects to which photographic illustrations are added. The conclusions can be summarized as follows: (a) Somatomotor reactions, in relation to dose and of less to more, may include the following phenomena: generalized fine tremor, myoclonias, hypercinetism with flight attitude and defensive aggression, incoordination and ataxia with falls forward, backward and sideways and convulsions that can bring death. When motor excitation syndrome decreases, an inverse state of inhibition may occasionally occur, although moderate and drowsiness. The nature of this whole picture participates in pyramid and extrapyramidal elements, with the latter being outstanding. (b) The neurovegetative response, also in relation to the dose and the route of incorporation, is characterized by the following phenomena: mydriasis with preservation of the photomotor reflex, sialorrhea, urination, defecation, emesis, piloerection and diaphoresis. These responses are very manifest and accompany somatomotor phenomena from the beginning. Its nature is complex. c) Haemodynamic response is characterized when the drug it is provided by the intravenous route, with a sudden low blood pressure, but with early recovery and accompanied by respiratory depression with occasional transient apnea. When using the intra-muscle track, tensional change is much smaller but more sustained. In both cases, as the normal level recovers, the breadth of ventricular capacity increases. d) It follows from all the above that the alkaloid is of high toxic power. The severity of the pharmacodynamic changes it produces makes its manageable area narrow.