Bovine corneal aldehyde dehydrogenase was purified to homogeneity and characterized with aldehyde substrates at pH 7.4. The enzyme was a dimer with a subunit size of 65 kDa. Using kcat/Km values as an indication of substrate efficacy, aldehyde products of lipid peroxidation were recognized as the likely 'natural' substrates. Protein yields from enzyme purification, as well as electrophoretic analyses of crude and purified enzyme preparations, demonstrated that this enzyme is the major soluble protein in bovine cornea, and constitutes around 0.5% wet weight of tissue. A dual role in protecting the eye against UV-B light is proposed--oxidation of aldehydes generated by light induced lipid peroxidation, and the direct absorption of UV-B light by bovine corneal ALDH.