The problem of photosensitivity produced by drugs has attracted great interest and has been the subject of many investigations since Tappeiner and Raab in 1900 first described the photodynamic reaction which occurs when paramecia in an acridine solution are exposed to light.1 The most significant advance in our understanding of drug photosensitivity since that time was brought about by the classical studies of Stephan Epstein concerning sulfanilamide photosensitivity in man in 1939.2 Epstein demonstrated 2 distinctly different mechanisms capable of producing photosensitivity to drugs. The first was a phototoxic reaction which occurred in all persons receiving adequate exposures to ultraviolet light following intracutaneous injection of sulfanilamide. The second mechanism was observed only in a very small number of those similarly exposed. It had the features of an allergic response and therefore was labeled a photoallergic reaction. W. Burckhardt, also working with sulfanilamide in man, confirmed Epstein's work shortly