THIS STUDY was initiated to determine whether in the treatment of streptococcal infections in children with oral penicillin the dose and frequency of administration recommended by the American Heart Association (250,000 units three times daily for ten days)1can be reduced without jeopardizing the efficacy of therapy. We also wished to determine whether (a) such a reduction in frequency of administration should be accompanied by an increase in total dosage, (b) an increase in dosage without decreasing the frequency of administration improved the effectiveness of therapy, and (c) how these changes in frequency of administration and total dose compared in effectiveness with an alternative recommendation of the American Heart Association, namely, a single dose of 600,000 units of benzathine penicillin G. Methods Subjects.—As in a number of our previous studies, children and an occasional parent from our private pediatric practice with bacteriologically proved beta hemolytic streptococcal illness were