The equation of some biochemical reactions to the genetic compounds of natural indolic hallucinogens has enabled some researchers to suggest a physiological role for some of these substances. Although not definitive, the few reactional cycles proposed have, in this context, an undeniable interest. It is important, however, to point out that pharmacologists, among others, have always worked with pure chemicals, while hallucinogenic extracts from plants by the natives, have a often very complex composition. In addition, the preparation of these extracts undoubtedly changes the relative concentration of the various compounds and, in some cases, reveals new alkaloids. At the level of the plant cell, the relations between the chemical structure and the biological activity of 3-indoyl-acetic acid - a standard phytohormone - and its derivatives are beginning to be sufficiently known. New experience, which will enable the biochemically and physiologically connect this auxin to hallucinogenic compounds of the same kind, will ensure, in the future, better knowledge of the biological properties of these indolic alkaloids.