Copper,zinc-superoxide dismutase (Cu,Zn-SOD) activities were determined by the chemiluminescence method using the cypridina luciferin analog (MCLA) in 22 human brains from fetuses to adults. Cu,Zn-SOD activity of the cerebral cortex and white matter increased from 15% in fetuses to 50% of adult levels in neonates. The activity of the white matter was higher than that in the cortex in the fetal period, but was essentially the same as those of the cortex in the postnatal period. Cu,Zn-SOD activity in the central nervous system was highest in the spinal cord and higher in the order pons, medulla oblongata > cerebellum, midbrain, thalamus > putamen, pallidum and cerebrum. These low activities may be related to the vulnerability of cerebral cortex and white matter in premature infants.