Since our1 first studies of the polymorphic light-sensitive eruptions were reported, an effort has been made to study further the clinical and microscopic means of differentiation of solar dermatitis and discoid lupus erythematosus. Sufficient time has elapsed to evaluate certain therapeutic ideas suggested in the earlier study, i. e., the value of hormonal therapy and the use of the antimalarial drugs such as chloroquine and quinacrine (Atabrine). Clinical Differentiation Clinical differentiation of plaque-like (the commonest type) polymorphic light eruption and discoid lupus erythematosus is not difficult in most cases and may be summarized as follows: The papular and prurigo-like type of polymorphic light eruption does not offer any confusion with lupus erythematosus; this is a rarer form of the disease. Some of the patients have had prurigo aestivalis since childhood. The line of division from the plaque-like variety, however, is most difficult in many cases