The effect of antibiotic therapy on the rate of resolution of signs and symptoms of streptococcal pharyngitis in children has not been previously evaluated in a placebo-controlled study. Patients were randomly assigned to penicillin or placebo therapy and reevaluated after 48 hours, at which time benzathine penicillin G was given to all patients. Rates of improvement in treated (17 patients) or control (18 patients) cases significantly favored treatment with regard to resolution of pharyngeal injection, tender cervical lymph node and total duration of fever. Symptoms of sore throat and the parents' assessment of the well-being of their children also significantly favored treatment. This study confirmed the clinical impression of physicians that specific antibiotic therapy promptly alleviates symptoms in most children with streptococcal pharyngitis.