Most investigators (Miescher,1 Urbach and Gottlieb2) consider contact dermatitis an expression of epidermal sensitivity; yet it has been known for a long time that in many cases of contact dermatitis there are often found positive reactions both to patch tests and to intradermal tests with the same material. These double forms of reaction to soluble simple chemicals have been noted by many observers, such as Frei,3 Blumenthal and Jaffé,4 Sulzberger,5 Nexmand.6 Paschen and Sulzberger7 reported tuberculin-type reactions to intradermal injections of an oily solution of ragweed oleoresin. Yet the significance of the dermal delayed sensitivity to simple chemicals has been stressed only by a few investigators, especially Haxthausen* and Epstein.† Cormia13 stated in 1938 that "in man the reaction of sensitivity may at times be elicited by both patch and intradermal tests; for example as in arsphenamine dermatitis, in