Local oxygen consumption of the rat brain cortex was artificially increased through local electrical stimulation of a small tissue sphere 5 mm in diameter. Measurements of the local PO2 distribution within the stimulated tissue as well as the induced field potential were performed with the same gold microelectrode. During stimulation the oxygen consumption increased significantly giving rise to local hypoxia and after 1-3 minutes to local anoxia depending upon the stimulus strength and duration. If however pronounced respiratory hypercapnia was applied the increased demand for oxygen was met by an increase in cerebral blood flow resulting in an almost constant PO2 level. According to these results it is concluded that the anoxic tissue sphere was not large enough to cause changes in the local blood flow. On the other hand recovery from local hypoxia and anoxia as well as reoxygenation of the stimulated tissue were delayed if a general hypoxia already existed.