Recurrent group A beta-hemolytic streptococcus (GABHS) pharyngotonsillitis related to penicillin failure presents a serious clinical problem. Failure to eradicate streptococci from patients can occasionally lead to rheumatic fever and rarely to glomerulonephritis. beta-lactamase-producing strains of aerobic and anaerobic bacteria in inflamed tonsils have been associated with increased failure rates of penicillins in the eradication of these infections. These organisms include Staphylococcus aureus, Haemophilus influenzae and H parainfluenzae, Moraxella catarrhalis, Fusobacterium sp, and pigmented Prevotella and Porphyromonas spp. The indirect pathogenicity of these organisms is apparent in their ability not only to survive penicillin therapy but also to protect penicillin-susceptible pathogens from that drug. These organisms have demonstrated the ability to protect GABHS in vitro and in vivo from penicillin. Numerous reports have described the successful therapy of recurrent GABHS tonsillitis with antimicrobials directed at both GABHS and the beta-lactamase-producing organisms.