Although the psychotomimetic indolealkylamines N,N-dimethyltryptamine, 5-methoxy-N,N-dimethyltryptamine, and 5-hydroxy-N,N-dimethyltryptamine have been unequivocally identified in human body fluids, evidence relating their concentration to the presence of psychotic illness in humans remains controversial. A series of studies on the metabolism of the compounds in the rat have highlighted the rapidity and with which these are metabolized and renally excreted. The implications of our observation for the interpretation of past clinical studies and the design of future ones is discussed.