The psychotic effects of N,N-dimethyltryptamine (DMT) and N,N-diethyltryptamine (T-9) have been compared with the effects of mescaline and LSD-25. The most outstanding features of DMT model psychosis are the rapid onset and the short duration of the symptoms. This may indicate a different mechanism of action from that of LSD and mescaline. New symptoms appearing with both tryptamine derivatives are the choreiform athetoid movements. This phenomon could be a new tool for investigating experimentally the mechanism of the extrapyramidal compulsive movements. The psychotic effects of tryptamine derivatives supports the aminotoxic and indole theory of schizophrenia.