Three pregnant albino Sprague-Dawley rats were subjected to simulated high altitudes of 18,000 feet (365 mm Hg) in low pressure chambers during their entire pregnancy. The brains of the newborn rats were removed immediately after birth and placed in 10% formalin. The brains were sectioned, stained, and analyzed for changes in the number of cells in the cerebral cortex of the frontal lobes. An equal volume of control material was similarly prepared and analyzed. A volume of tissue of about one-fourth cubic millimeter was used in the control and in the experimental tissue. The results indicated a 19.29% increase in the number of cells in the frontal cortex of newborn rats subjected to simulated high altitude anoxia. This increase is believed to be due to a proliferation of glial elements in the areas of the cortex which were studied. The cell hyperplasia seen here may be a response to physiological stresses placed upon the fetus by maternal anoxia.