This study reports bacterial specimens obtained from 112 children presenting with a ruptured appendix. Additional samples were studied from 11 of these patients who developed a postoperative surgical draining wound. Bacterial growth occurred in 100 peritoneal fluid specimens. Anaerobic bacteria alone were present in 14 specimens, aerobes alone in 12, and mixed aerobic an anerobic flora in 74 specimens. There were 144 aerobic isolates (1.4 per specimen). The predominant isolates were: E. coli (57 specimens); alpha-hemolytic steptococcus (16 specimens); gamma-hemolytic streptococcus (15 specimens); Group D streptococcus (12 specimens); and P. aeruginosa (9 specimens). There were 301 anaerobic isolates (three per specimen). The predominant isolates were: 157 Bacteroides spp. (including 92 B. fragilis group and 26 B. melaninogenicus group); 62 gram-positive anaerobic cocci (including 30 Peptococcus sp.; 29 Peptostreptococcus sp.); 27 Fusobactenium sp.; and 16 Clostridium sp. B. fragilis and Peptococcus sp. occurred in 23 patients. Beta lactamase production was detectable in 98 isolates recovered from 74 patients. These included all isolates of B. fragilis and six of the 23 Bacteroides sp. Forty-nine organisms (16 aerobic and 33 anaerobic) were recovered from the draining wounds. The predominant organisms were: B. fragilis (8 specimens); E. coli (6 specimens); Peptostreptococcus sp. (5 specimens); and three specimens each of P. aeruginosa and Peptococcus sp. Most of these isolates were also recovered from the peritoneal cavity of the patients. These findings demonstrate the polymicrobial aerobic and anaerobic nature of peritoneal cavity and postoperative wound flora in children with perforated appendix, and demonstrate the presence of beta lactamase-producing organisms in three-fourths of the patients.