The experimental psychosis observed after drinking Ayahoasca, a South American hallucinogenic beverage from the Amazon Indians, reproduces the pathologic transmethylation theory of schizophrenia. This theory postulates a decrease in the monoamine oxidase (MAO) activity, which results in the accumulation of methylated indolealky- lamines, such as bufotenin (5-hydroxy-N,N-dimethyltryptamine), N,N-dimethyltryptamine (DMT) and 5-methoxy- N,N-dimethyltryptamine. These substances are strong hallucinogens as has been previously confirmed experimentally. On the other hand, it is known that Ayahoasca is a beverage usually prepared by boiling two plants, one of them rich in beta-carbolines, which are naturally occurring strong inhibitors of MAO, and the other with high quantities of DMT. This particular combination reproduces what is supposed to occur under pathologic conditions of different psychoses. The effects of Ayahoasca were studied in subjects, assessing urine levels of DMT by gas chromatography-mass spectrometry (GC-MS) before and after the intake of the beverage. The results of this study confirm that the hallucinogenic compounds detected in the healthy subjects’ (post-Hoasca, but not before) urine samples are the same as those found in samples from acute psychotic unmedicated patients. The chemical composition of the Ayahoasca beverage, and of the plant material used for its preparation are also reported as well as psychometric and neuroendocrine subject parameters.