Regional distribution of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase activities were studied in 22 anatomic sites of 5 human brains. No significant regional differences were observed in cytosolic activities of any enzyme studied, nor in particulate activities of superoxide dismutase, catalase and glutathione reductase, whereas particulate glutathione peroxidase activities were distributed unevenly, the highest activities observed in the basal nucleus and amygdala. There were significant interindividual differences in the activities of each enzyme. This was shown to result partly from the decrease of cytosolic superoxide dismutase and catalase activities with age, concurrently with age-related decrease of particulate glutathione peroxidase and glutathione reductase activities.