Beta-lactamase production by the normal pharyngeal flora could account for the failure of penicillin treatment in patients with recurrent tonsillitis. We studied the microbial flora of tonsils from 22 healthy children (control group) and from 40 children with recurrent tonsillitis who were treated with penicillin. Cultures were made before treatment and repeated 15 days after the first culture. Streptococcus pyogenes was recovered in 25% of the patients in the recurrent tonsillitis group. Beta-lactamase producing bacteria were recovered in 100% of children with tonsillitis and in 86.4% of the healthy children. We found a 65% failure rate of penicillin therapy in recurrent tonsillitis. Our results suggest that beta-lactamase production by pharyngeal organisms does not fully explain the failure of penicillin therapy for recurrent tonsillitis.