In 1925, I published an article1on the treatment for psoriasis by an ointment of crude coal tar and ultraviolet light. This treatment has given far better results than any method I have ever used. The advantages that I claimed for this treatment were its uniform effectiveness, its lack of danger and even untoward symptoms, its nondestructive character, its accessibility and its comparative cheapness. Further experience justifies these claims, and in some respects establishes the method as being unique in its therapeutic results. DEVELOPMENT OF THE METHOD OF TREATMENT It has long been known that most patients with psoriasis are better in summer than in winter, that a sojourn in a locality with much sunshine is beneficial, and that sunbaths alone will clear up some attacks. Therefore, it was argued that if it were possible to sensitize the patches artificially, the response to light should be more