We have studied the development of ocular aldehyde dehydrogenase (ALDH) and alcohol dehydrogenase (ADH) activities in C57BL/6J inbred male mice. Eyes were removed from freshly killed mice, enucleated, extracted, and analyzed for enzyme activities for animals of various ages during neonatal development, up to the adult stage. Activity levels were compared between mice maintained from birth in either complete darkness or on a 12-hour light/dark cycle. Ocular ALDH activity increased dramatically (greater than 30-fold) during the first 3 weeks of life. Moreover, light-adapted animals showed significantly higher ALDH activities from day 8. Ocular ADH activity also increased during development (greater than 5-fold) although the profile showed a steady increase to reach adult levels. Light-adapted mice showed no significant differences in ADH activity up to the weaning stage, as compared with mice maintained in darkness. These observations support proposals from earlier studies for major functional roles for both corneal ALDH and ADH in protecting the eye against ultraviolet light-induced damage.