Putrescine, spermidine and spermine levels were detected in the retina, visual cortex, cerebellum and parietal cortex of CD1 mice exposed to 36h continuous light or darkness. Retinal putrescine and polyamine concentrations were found to be highest in dark-adapted mice, and the stimulation of dark-adapted retina with flicker illumination was also accompanied by a significant decrease in putrescine, spermidine and spermine levels. In visual cortex as well as in cerebellum spermidine and spermine contents were higher in dark-adapted mice in comparison to light-exposed animals, while in parietal cortex no significant change was found neither in spermidine nor spermine levels. In the brain areas studied flicker illumination produced no significant decreases in putrescine and polyamine contents. The total polyamines expressed as putrescine equivalents were noticeably decreased in retina, visual cortex and cerebellum of light-adapted mice. In the retina spermine/spermidine molar ratio was significantly higher than in dark-adapted mice. The administration of N1, N2-bis-(2,3-butadienyl)-1,4-butanediamine (MDL 72527) produced a strong decrease of retinal putrescine and spermidine concentrations in both dark-adapted and light-exposed mice, and in the retina of mice exposed to continuous light a significant decrease in the spermine level was also observed. According to the influence on polyamine reutilization, after the irreversible inhibition of polyamine oxidase by MDL 72527, in the retina N1-acetylspermidine and N1-acetylspermine accumulation was highest in light-adapted mice. On the contrary in visual cortex, cerebellum and parietal cortex the MDL 72527 administration produced a more marked decrease of putrescine and spermidine contents in mice kept in continuous darkness.