Traditional concepts regarding the bacteriology and therapy of nonbullous impetigo have been reexamined. Although in the United States the disease is considered primarily of streptococcal origin and amenable to penicillin therapy, we found that Staphylococcus aureus was the most common isolate in 71 patients studied. Only two patients yielded pure cultures of group A beta-hemolytic streptococci. All but two isolates of S. aureus were resistant to penicillin; one of these two isolates was also resistant to erythromycin. Erythromycin appeared to be more efficacious than penicillin for the treatment of impetigo.