1. Exposure of cells to ultraviolet light induces molecular changes in DNA which may lead to cellular death. 2. One product, pyrimidine dimers, is reversed during subsequent exposure to visible light by photoreactivating enzyme. 3. Photoreactivating enzyme has been recorded in different organisms, but inconsistencies in its distribution suggest it may have other functions. 4. We have found photoreactivating enzyme in the blind cave dwelling fish, Anoptichthys jordani. 5. Sufficient time has elapsed in the cave environment to allow loss of features of importance to epigean fish, including the eyes and pigmentation. 6. The continued presence of the enzyme indicates that it may have other functions.