One hundred patients with impetigo were prospectively enrolled in a study to determine the current etiology and comparative therapeutic efficacy of two oral antimicrobial agents active against both group A beta-hemolytic streptococci (GABS) and Staphylococcus aureus. After obtaining a bacterial culture from a representative impetiginous lesion, the children were randomized to receive 10 days of either erythromycin (40 mg/kg/day) or dicloxacillin (25 mg/kg/day). S. aureus alone was isolated from 46 children, and in association with GABS from 25 children. GABS alone was isolated from nine patients. Of the 59 evaluable children with S. aureus isolates, 28 of 29 treated with erythromycin and 29 of 30 treated with dicloxacillin were cured or improved on follow-up examination. Thus, we conclude that erythromycin is the drug of choice for impetigo in our midwestern locale because of its high efficacy and relatively low cost.