Streptococcal eradication rates of 86% were demonstrated in 97 patients seen on day 14 and in 73 patients seen on both days 14 and 28 after a ten-day course of erythromycin estolate therapy given at a dosage of 20 mg/kg/day, administered in two equal doses. The efficacy of this regimen compares favorably with other results in which this and other erythromycin preparations have been employed at higher doses, usually in the range of 30 to 50 mg/kg/day. Our reported effectiveness at a lower than usual dose of erythromycin is probably explained by the following factors: the known susceptibility of group A streptococci to low concentrations of erythromycin, the uniform absorption of the estolate formulation of erythromycin, and adequate compliance in adhering to the treatment regimen by the majority of our patients. This dosage schedule of erythromycin is simple to administer; and a reduction by half of the total dose usually recommended provides an economical advantage for patients.