Hooded rats prenatally exposed to mild carbon monoxide hypoxia were studied as adults. Flash evoked potentials were recorded from the visual cortex of unanesthetized exposed and control rats at four different flash intensities. The amplitude of bothe the P1-N1 and N1-P2 components on the flash evoked potential were significantly greater in CO-exposed female rats than in control females. The experiments thus demonstrate long term alterations in CNS function from exposure to relatively mild levels of CO.