The evidence linking acute nephritis and infection of the throat or skin with certain types of group A beta-haemolytic streptococci is of three kinds: (1) studies of streptococcal disease when acute nephritis was more prevalent than usual, (2) cultures from the throats of established cases of acute nephritis, and (3) serological studies of such cases for type-specific antibodies.Examples of the first are the reports of Manser and Wilson (1952), Reed (1953), Kleinman (1954), Seigel et al. (1955), Stetson et al. (1955), and George et al. (1958. Studies of established cases of acute nephritis have been reported by Rammelkamp and Weaver (1953), Wertheim et al. (1953), Wilmers et al. (1954, Hardin et al. (1956), andBernstein andStillerman (1960). Two investigations on the production of type-specific antibodies are noteworthy-those of Cullhed et at. (1959) and of Earle and Jennings (1959 (Ravenswaay, 1944, Rantz et al., 1945. In assessing the significance of such isolations it is essential to know the prevalence of different types in the community from which the cases are drawn. There are, however, few reports on the relative incidence of different types in acute pharyngitis in normal populations; what evidence there is suggests that type 12 is widely prevalent (Siegel et al., 1961 ; Mitchell, 1962Valkenburg et al., 1963.Moreover, the literature abounds in anomalies. Acute nephritis is said to be twice as common in males (Seegal et al., 1935 ;Earle and Seegal, 1957) has since appeared.We report here a prospective study in a normal community: in a small town and the neighbouring countryside, virtually the whole population of which is under our care. In 1959 this population numbered approximately 14,000 persons; the study began on 28 January of that year and continued for 12 months. * General Practitioners, Rugeley, Staffs.The objects were: (1) to determine the prevalence of different types of streptococci found in association with acute sore throat, (2) to uncover cases developing acute nephritis or urinary abnormalities after streptococcal pharyngitis, and (3) to relate them to the type of Streptococcus pyogenes isolated at the patient's first attendance. MethodAll patients with symptoms or signs of sore throat were admitted to the study. The throat was swabbed when the patient was first seen, and specimens of urine were tested. After three months it became necessary to reduce the number of urine specimens tested, and patients were asked thereafter to send in one specimen when first seen, and a second three weeks later. For the first nine months information (including details of temperature and treatment) was recorded on special cards; recording was then simplified and such details were omitted.Urines were tested by heat and acetic acid; if protein was found the urine was centrifuged and the deposit examined microscopically.Throat swabs were sent by post to the Public Health Laboratory 10 miles (16 km.) away (usually arriving within 24 hours) and were sown on to horse-blood agar plates, which were incubated aerobic...