While investigating the effect of therapeutic doses of reserpine on the urinary excretion of tryptamine in schizophrenic patients, we observed an abnormally high level of that indoleamine during periods of increased psychotic activity.1This finding prompted a further study of a possible relationship between indoleamine metabolism and behavior. The present report on 20 male schizophrenic patients is concerned with the average urinary excretions of tryptamine and total indole-3-acetic acid during periods without treatment and also with reserpine medication, as well as with the excretion of these indole derivatives during different degrees of psychotic activity. Method The patients selected for this study were in good physical health and were good eaters. To allow close supervision, they were studied in 4 different groups, each patient for an average of 42 days. One week previous to the study and during the entire period of investigation, the patients received