It has long been alleged that the ultraviolet portion of sunlight contributes etiologically to the development of carcinoma of the skin. However, the exact mechanism of action whereby and the degree to which ultraviolet influences carcinogenesis have never been clarified in humans. One controversial issue has been the protective role of melanin in the skin. In addition there has been disagreement as to whether the initial detrimental changes from ultraviolet light are within the dermis or epidermis. Most studies on ultraviolet penetrability in human skins have been carried out on bullae created by various methods, including solid carbon dioxide and cantharidin.1,2 By these studies the average penetrability of ultraviolet light into the dermis has been from 6% to 10%. Bachem and Reed1 measured differential layer absorption of different wavelengths within the ultraviolet spectrum in human skin, and found that the stratum corneum absorbed most of the ultraviolet light