SUMMAkV!hc discovery, approxifualely a century a\<(), o/ the role played by solar nlfraviolel railiation in delertuinin^ the state of the skin's heail/i. nuich proi^ress has been made in guiuini; a more exact iinderstandinii of the relationship which exists between .\kiii and sun. In this review there has been an attempt to trace the discoveries thai have been made towards interpreting the physical and chemical reactions responsible for the ileveh'j'nu'Ut of ultraviolet erythema in the skin. Consideration has been i^iven to such factors as the intensity and duration of radiation, the specific wavelcnf^tlis involved, the mechanism of the inflammatory response and the relative susceptibility of difjerent skin types. Other forms of skin damai^e in relation to solar erythema are also considered. the development and comparative efjeclivcness of the body's natural defence .systems af^ainst this erythema has been discassed in so far as prcseni l