A number of synthetic, possibly naturally occurring, psychotogenic indolic compounds have been of interest to investigators for many years.1 In addition, there have been a large number of studies covered in recent reviews on "abnormalities" of indole compound excretion in various mental disorders, including: phenylketonuria, Hartnup's disease, pellagra, Huntington's chorea, porphyria, and both the affective and schizophrenic psychoses.2-4 The inconsistencies of findings, particularly in the area of psychoses in the face of continued studies finding significant differences, suggested to us the possibility that extraneous variables might have been operating in a systematic way to produce these results. In a series of studies undertaken to explore some of these, we have demonstrated the importance of controlling for urine volume, general dietary habits, amount of tryptophan in the diet, the time of sample collection and bowel flora. In addition, while studying the potential role of nonspecific stress factors, we have