During a 24-month period, throat-swab cultures were obtained on 1,362 well children who were 3 months to 14 years of age. The overall incidence of positive cultures for group-A beta-hemolytic Streptococcus was 3.3%; in those children older than 1 year, it was 4.4%. The largest incidence of positive cultures occurred in the 5- to 7-year-old (8.3%) and 8- to 10-year-old (4.5%) age groups. No positive cultures were obtained from 339 infants younger than 1 year of age. There was no relation between positive cultures and the month of the year. There were no significant differences between the age, sex, presence of tonsils, previous group-A streptococcal infections, or the presence in a daycare center or school of children with positive cultures compared with those children with negative cultures. Follow-ups were obtained on 29 of 45 children with positive throat cultures; all of the children were asymptomatic and had normal results of physical examinations. Group-A streptococci of the same serotype as the original isolate were isolated from 19 of these children. Three to four days after a ten-day course of erythromycin estolate, five of 19 children again had positive cultures. Twenty-six of the 29 children had a total of 43 siblings residing in the home. Serotypically identical group-A streptococci were isolated from five siblings (11%). Only one of 29 patients from whom paired serum samples were obtained showed a fourfold rise or fall in the Streptozyme titers.