1. Subcutaneous injection of adrenaline into normal male volunteer subjects caused large increases of plasma non-esterified fatty acids and free tryptophan, but plasma total tryptophan fell considerably. Therefore increases of the percentage of plasma tryptophan in the free state were more marked than absolute increases of free tryptophan.
2. Plasma tyrosine fell slightly and plasma phenylalanine and cortisol were unaffected.
3. It is suggested that catecholamine release could lead to abnormalities of tryptophan disposition in stress and psychiatric illness.