THE VIGOROUS treatment of streptococcal infections to prevent the sequelae of rheumatic fever and acute glomerulonephritis has received considerable emphasis in recent years. Early, a,ccurate diagnosis of group A streptococcal infections associated with the complications, however, has not kept pace with therapeutic advances. Physicians often experience considerable delay in obtaining a laborat,ory diagnosis and must administer therapy to acute throat infections without knowing the etiological agent. The delay is due to the necessity of isolating a pure streptococcal culture, with subsequent preparation of extracts for use in precipitin grouping tests. Though beta hemolytic streptococcal organisms can be identified readily and quickly, the correct designation of the infecting streptococcal group requires several more days of testing. Coons and his associates first described in 1942 a technique of bacterial identification which might offer rapid diagnosis (1). This was the fluorescent antibody technique, described more definitively in subsequent writings by Coons and Kaplan as an antigen-antibody reaction to identify miumps virus, pneumococcal polysacca,rides, and rickettsia (2). Moody, Goldman, Thomason, and Cherry applied this same method to the identification of other organisms (3-5). Mooidy, Ellis, and Updyke first developed an accurate method for the identification of streptococci using the fluorescent antibody technique (6). They showed that specific fluorescent antibody could be prepared and used for grouping streptococci in dried smears by staining only group A streptococci and also that a specific fluorescein-labeled antibody could be used to identify groups B, C, D, F, and G. Occasional cross reactions between organisms of groups A, C, and G were corrected by absorbing group A fluorescent antibody with grolup C organisms. This did not affect in any way the affinity of the antibody for group A cells. As a result of this discovery, we proposed a study of the fluorescent antibody technique for streptococca,l identification under field conditions using the facilities of a local health department. The study was conceived on the principle that the technique would give private physicians a diagnosis on suspected group A streptococcal disease within 4 to 5 hours after a specimen was submitted rather than the 3 to 5 days ordinarily required. The experimental design emphasized quality and correctness of technique rather than performance of a large number of tests. Funds for the study were supplied by the Heart Disease Control Branch of the Public Health Service, and technical supervision, as well as the various reagents used in performing the tests, was provided by the Special Research Unit of the PHS Communicable Disease Center. The bureau of laboratories of the Maryland Department of Public Health, the Montgomery