<正> Histochemical study and determination of cytochrome oxidase （CTO） relative activ-ity with a Leitz MPV-III microspectrophotometer in different regions of normal rat brain werecarried out.9 healthy male Wistar rats were divided randomly into 2 groups;an enzyme activi-ty studied group and a control group with HE staining.It was found that 2 kinds of CTO distri-bution areas exist in the brain of rats;the high activity area including cerebral cortex

corpusstriatum （gray matter）

thalamus

cerebellar cortex

etc

and low activity area including corpuscallosum

corpus striatum （white matter）

hippocampus

cerebellar white matter

etc.The dif-ference of CTO activity between the 2 areas is statistically significant （P<0.01）.Moreover

according to the intensity of positive response to CTO detecting stain

the granular layer of thecerebellum can be classified as cytochrome oxidase richly-contained area（CTORA）orcytochrome oxidase poorly-contained area （CTOPA）.The CTO activity of the former issignificantly higher than that of the latter（P<0.01）.