Groups of skh-1 (albino) and Skh-2 (pigmented) hairless mice were irradiated for 125 hr using a modified GE F8T5-BL black light with and without a 3-mm plate glass filter to remove light below 320 nm. The epidermis was examined by forward scattering and by histological section postirradiation at 48 hr, 96 hr, 9 days, and 23 days. Changes in the epidermis of all animals were compared to control groups. Although no differences were seen between Skh-1 and Skh-2 mice, both the magnitude and shape of the forward scattering absorption curves were changed by the irradiation used. In both strains, differences which were detected at 48 hr postirradiation had returned to normal visually by 23 days, with no augmented pigmentation occurring in Skh-2 animals. At 23 days postirradiation, however, residual optical alterations were observed. This phenomenon, detected optically, may be skin acclimatization.