The concentration of glutathione in the rat cerebral cortex, cerebellum and liver was examined during postnatal development. The glutathione level in both brain regions was low at the earliest age studied (postnatal day (PND) 3) and peaked at PND7. In the liver, the glutathione level was maximal at PND30. The glutathione peak at PND7 occurs during a period of intense synaptogenesis and may be related to a neuroprotective role during brain development.