Post-ultraviolet radiation (UVR) treatment of the South American opossum, Monodelphis domestica with long-wavelength radiation (320-400 nm) suppressed the induction of histopathological alterations in the skin. This study identifies DNA as a primary chromophore involved in the induction of various photobiological responses of the skin such as hyperplasia and sunburn cell formation, and also identified pyrimidine dimers as one responsible DNA lesion. The histology of skin from opossums exposed to multiple doses of UVR showed that pre-malignant changes had occurred in the skin