The effects of acute or repeated administration of indole-pyruvic acid (IPA), a keto-analogue of tryptophan (TRP), were studied in various brain areas of rats by measuring the changes of 5-hydroxytryptamine (5-HT) and of norepinephrine (NE) content and metabolism. The analgesic and sedative properties of the molecule were evaluated by measuring the tail-flick latency, the spontaneous activity and the potentiation of the barbiturate-induced sleep. Acute or repeated administrations of IPA (20 or 50 mg/kg) increased the utilization of 5-HT in the cortex, hippocampus, diencephalon and brain-stem of rats fed a standard laboratory diet. IPA, however, did not substitute TRP in rats fed a TRP-free diet. The administration of this keto-analogue resulted also in a decreased content of 3-methoxy-4-hydroxy-phenylglycol (MHPG) in the cortex and in the brain-stem, thus suggesting a decreased utilization of NE in these areas. Furthermore, IPA administration decreased the rats' spontaneous activity, increased the duration of barbiturate-induced sleep and increased the tail-flick time, thus indicating that it has sedative and analgesic properties.