The author examines in detail the symptomatology, diagnosis, and treatment of plague, and outlines the problem of the length of the incubation period.The clinical features commonly met with in all severely-affected plague patients, regardless of the primary localization of the infection, are described. The author then deals with the symptomatology and manifestations of bubonic plague as compared to those of primary pneumonic plague.The importance of a clinical diagnosis, from the point of view of prevention, is stressed, and the differential diagnosis of various forms of the disease is described.The study contains a detailed discussion of the respective merits of antibiotic treatment, serotherapy, and sulfonamide treatment. The author points out that the outstanding success of streptomycin and some other antibiotics will probably relegate the sulfonamides to the second rank in the treatment of bubonic plague.