The designation "physical allergy" was applied by Duke1 to "the symptoms bronchial asthma, vasomotor rhinitis and conjunctivitis, photophobia, abdominal pain, erythema, pruritus, urticaria, angioneurotic edema, eczema and shock" caused "specifically and solely by the action of a physical agent, such as light, heat, cold, mechanical irritation, freezing and burns and, in the case of heat sensitiveness, indirectly by mental and physical exertion." Perhaps the most familiar of these manifestations are urticaria excited by cold and by heat, which Duke divided into three types: (1) general urticaria provoked by heat, physical exertion or emotional excitement, (2) local urticaria provoked by heat and (3) local urticaria provoked by cold. The first type seems of great interest because Grant, Pearson and Comeau2 have presented convincing evidence that the lesions are produced by the release of acetylcholine at the terminations of cutaneous nerves. This is the first demonstration of a mechanism by