This report of an outbreak of streptococcic sore throat in an army camp is made because there were clinical and epidemiologic features of unusual interest. BACKGROUND The outbreak occurred on June 17, 1942 and the next succeeding few days in a Western army camp. The camp is an assembly center for troops coming from various parts of the country. It is situated in a flat area; the weather is hot and dry in June, and ordinarily there is no streptococcic sore throat during this season. At the time of the outbreak the camp was still partly under construction. THE OUTBREAK The outbreak began with explosive suddenness at a time when there was no illness in the camp. There were, however, a number of men who had had "tonsillitis" at other establishments within the past few weeks before coming to this camp. The number of men reporting sick each day is