Human aldehyde dehydrogenase isozymes (ALDHs; EC 1.2.1.3) exhibit very high levels of activity in anterior eye tissues. Human corneal ALDH1 and ALDH3 isozymes are present as major soluble proteins (3% and 5%, respectively, of corneal soluble protein) and may play major roles in protecting the cornea against ultraviolet radiation (UVR)-induced tissue damage, as well as contributing directly to ultraviolet B (UV-B) photoreception. The human lens exhibits high levels of ALDH1 activity (1-2% of lens-soluble protein) and lower levels of ALDH3 activity. Kinetic analyses support a role for these enzymes in the metabolism of peroxidic aldehydes, which have been reported in ocular tissues.