Within the last three years, dinitrophenol burst upon the medical world with meteoric suddenness. The groundwork was laid as early as 1885,1when the effects, on the dog, of dinitro-alpha-naphthol (a compound closely related to dinitrophenol) were studied. Interest in the drug lapsed until the World War, when poisoning of those working with it in munition plants was frequent.2Since 1933,3when its possibilities, especially in the treatment of obesity, were first spread before physicians, the drug has enjoyed a phenomenal growth in usage. Recently, Tainter4has given as an estimate that 100,000 patients are taking, or have taken, dinitrophenol. A detailed study of the voluminous literature on dinitrophenol reveals surprising gaps in our knowledge of the drug. Although our knowledge of the pharmacology and clinical actions of the drug rests on a secure footing, studies of its clinical pathology are wofully inadequate. Accordingly, this paper