Methods for identification of bacteria, viruses, and mycoplasmas were used to study pharyngitis in patients from a pediatric practice. Etiologic agents were recovered from 50% of 715 cultures from patients with pharyngitis and from 22% of 206 cultures from asymptomatic household contracts. Pharyngitis was diagnosed most often in children ages 6 through 8 years, and over one half of these illnesses were associated with group A streptococcus infections. Viruses were the most important cause of pharyngitis in infants, and Mycoplasma pneumoniae was associated with pharyngitis in early adolescence. Disease produced by viruses or M pneumoniae could not be distinguished from classical streptococcal pharyngitis. Mycoplasma hominis, which has produced exudative pharyngitis in adult volunteers, was not recovered from persons in this investigation; however, in other studies performed concurrently, M hominis was isolated from 0.5% of subjects including three adults with pharyngitis.