Ketamine, 2-(0-chlorophenyl)-2-(methylamino)-cyclohexanone, is a general anesthetic which on awakening produces psychic disturbance correlated with the metabolism of serotonin.

Since it is know that acupuncture increases cerebral serotonin, the blood levels of total and free tryptophan, its precursor, were studied in healthy volunteers to find out if the anti-hallucinatory action of acupuncture is dependent on an increase in cerebral serotonin.