The general outline of the thesis is given in the preface. The first two chapters review the ethnobotany, phytochemistry and psychopharmacology of ritual intoxicating enernas and snuffs among the aboriginal inhabitants of the western hemisphere. They are supplemented by a third chapter, which gives a general outlook on some factors to be taken into consideration in the muIt idisciplinary approach to ritual intoxicating plants. Chapter one is an overview of intoxicating enema rituals in the western hemisphere. Part one discusses ethnobotanical, chemical and psychopharmacological aspects. The following categories of ritual enema ingredients arise from this multidisciplinary approach: 1) It is weIl established that the plant provides one or more psychoactive principles and the Indian use of the plant as a ritual enema ingredient is confirmed or is quite probable: Agave, Anadenanthera, Brugmansia. 2) rt:[S weIl established that the plant provides one or more psychoactive principles, but the Indian use of the plant as a ritual enema ingredient is not weIl recorded or is even unlikely: Banisteriopsis. Datura, Ilex guayusa, Lophophora williamsii, Nicotiana. 3) The Indian use of the plant as a ritual enema ingredient is confirmed or is quite probable, but it is not weIl established that the plant provides one or more psychoactive principles: none. 4) The Indian use of the plant as a ritual enema ingredient is not weIl recorded, and it is not weIl established that the plant provides one or more psychoactive principles: Capsicum. Part two discusses the rectal pharmacokinetics and efficacy of possible ritual enema constituents. The literature yields convincing clinical evidence that caffeine and nicotine are effective following rectal application. A good rectal efficacy could also be expected from mescaline and from tropane alkaloids, but this is a hypothetical view which still awaits experimental confirmation, In self-experiments, ethyl alcohol produced substantial blood levels via the rectal route, but dimethyltryptamine did not produce any effect when parenterally active quantities were taken as an enema. First-pass elimination is the most likely explanation for the observed inactivity of dimethyltryptamine via the rectal route. Part three reports the chemistry of paricá seeds of the Brazilian Mau~ Indians. These seeds date from the first half of the 19th century, and seem to be t'he only ethnobotanical material from the western hemisphere, which has ever been directly associated with ritual rectal intoxication. Despite their considerable age, the seeds still y ielded as much as 15 mg/g of the Anadenanthera alkaloid bufotenin. This analytical finding supports the botanical view that the seeds are Anadenanthera seeds. Part four discusses enema scenes on classic Maya pottery. These scenes undoubtedly represent rituals and may very well indicate that the ancient Maya took intoxicating enemas in a ritual context. This idea is quite contrary to the traditional view that the ancient Maya were a contemplative people, who did not indulge in ritual ecstasy. The occasional display of vomiting actors would seem to provide a plausible reason why the Maya opted for rectal application. Some scenes present a fair amount of evidence that an alcoholic beverage may have been taken rectally. Other scenes open up the possibility that tobacco and the water lily may have served as an enema ingredient. It is sometimes speculated that the latter plant is hallucinogenic, but pharmacological confirmation of this view is still awaited. Chapter two is an overview of intoxicating snuff western hemisphere. rit~ls in the Part one discusses ethnobotanical, chemical and psychepharmacological aspects. The following categories of ritual snuff ingredients arise from this multidisciplinary approach: 1) It is well established that the plant provides one or more psychoactive principles and the Indian use of the plant as a ritual snuff ingredient is confirmed or is quite probable: Anadenanthera, Erythroxylum, Nicotiana, Virola. 2) It is well established that the plant provides one or more psychoactive principles, but the Indian use of the plant as a ritual snuff ingredient is not well recorded or is even unlikely: Banisteriopsis, Cannabis, Datura, Ilex guayusa. 3) The Indian use of the plant as a ritual snuff ingredient is confirmed or is quite probable, but it is not well established that the plant provides one or more psychoactive principles: Justicia pectoralis, pagamea macrophylla, Tanaecium nocturnum. 4) The Indian use of the plant as a ritual snuff ingredient is not well recorded, and it is not well established that the plant provides one or more psychoactive principles: Acorus calamus, Capsicum, Maquira sclerophylla, Piper interitum. ----- Part two discusses the nasal pharmacokinetics and efficacy of possible ritual snuff constituents. The literature yields convincing clinical evidence that atropine, cocaine, nicotine and scopolamine are effective following nasal application, but experimental confirmation of the efficacy of nasal tryptamine alkaloids is still awaited. This seems to be due, at least in the case of dimethyltryptamine, to the testing of low and therefore inadequate doses. In self-experiments, caffeine produced substantial plasma levels via the nasal route, but harmine, when 40 mg was taken as a nasal powder, did not produce measurable plasma levels. Without additional experiments, it is difficult to give a definite explanation for this negative result. Part three reports the chemistry of two yopo snuffs of the Venezuelan Piaroa Indians. One snuff yielded 10 mg/g of bufotenin, and the other one contained traces of harmine and of bufotenin. The isolation of harmine is quite significant, since this Banisteriopsis alkaloid is only rarely found in South American snuffs. Chapter three provides a general outlook on the multidisciplinary approach to native ritual plants by reviewing some botanical, chemical and pharmacological factors, which should be taken into consideration with this approach. With respect to botanical aspects, emphasis is laid on the importance of voucher specimens, on the Qsefulness of material in museum cOllections, on geographical predilection, and on nonpharmacological terminology in ethnobotanical references. Significant chemical factors are a careful selection of the studied material, and the specificity, sensitivity and reactivity of the analytical procedure. The pharmacological discussion focuses on experimental design and on common differences between native and experimental drug taking: clinical data are mostly obtained by testing an isolated constituent instead of the whole indigenous dosage form and this constituent may be administered in another dose and by another route of administration. It is argued that ethnopharmacology deserves a branch called ethnopharmacokinetics which must be aimed at the fate of indigenous drug constituents in the body. Some points in chapter three are illustrated by separate appendices. Appendix F provides an ethnobotanical survey of the ritual plants and reputed botanical intoxicants of New Guinea natives. The enumeration of thirty-seven different genera suggests that New Guinea practices are underrepresented in those general reviews on ritual botanical intoxication, which do not use pharmacological validity as a strict criterion for inclusion. Appendix G gives multidisciplinary information on fifteen different genera, all of which are established or suggested ingredients of ritual fumigatories in Middle and South America. Taken together with chapter one and chapter two, this appendix demonstrates the enormous variety in non-oral ritual intoxication among Latin American aboriginals.