Two hundred and ninety-eight consecutive patients with scarlet fever admitted to this activity during June and July 1945 were observed for (1) the degree of toxemia on admission, (2) the type of streptococcus present in the throat, (3) the response to various methods of treatment and (4) the incidence and types of complications. The patients were grouped according to treatment methods, and comparable groups were made up of alternately admitted patients. All patients were free from complications when admitted, and the rash had been present less than thirty-six hours. All convalescent serum used in these cases was made from blood drawn from convalescent scarlet fever patients on the eighteenth day of the illness. METHOD OF STUDY Grouping of Cases and Treatment Used.— Groups A1 and A2: A comparison of convalescent serum and antistreptococcus (horse) serum. Fifty of the first 99 patients were given 50 cc. of human convalescent scarlet fever