Aerobic and anaerobic microbiologic factors and recovery of beta-lactamase producing bacteria from obstetric and gynecologic infection. Specimens obtained from 736 patients with obstetric and gynecologic infections were studied for aerobic and anaerobic bacteria. Bacterial growth was present in 714 specimens. These included 53 specimens of infected fallopian tubes, 470 of infected endometrium, 94 of infected amniotic fluid, 57 of aspirates of cul-de-sacs in instances of pelvic inflammatory disease, 14 labial and vaginal abscesses and 26 of Bartholyn's cyst abscess. A total of 2,052 isolates (2.9 per specimen), 1,139 anaerobes (1.6 per specimen) and 913 aerobic or facultative (1.3 per specimen) were recovered. The most commonly isolated anaerobic bacteria was Bacteroides species (566 isolates), which included Bacteroides bivius (151), Bacteroides fragilis group (130), Bacteroides melaninogenicus group (110) and Bacteroides ureolyticus (47). Others included an anaerobic gram-positive cocci (391), Clostridium species (48) and Fusobacterium species (36). The most frequently recovered aerobic and facultative bacteria were Lactobacillus species (169), Escherichia coli (85), Neisseria gonorrhoeae (62), Staphylococcus aureus (59) and Group B streptococcus (55). Three hundred and sixty-five (18 per cent) of the isolates recovered from 276 (39 per cent) patients were beta-lactamase producing organisms (BLPO); 222 (61 per cent) anaerobes and 143 (39 per cent) aerobes or facultatives. The most common BLPO were B. fragilis group, B. bivius, B. melaninogenicus, B. disiens, Enterobacteriaceae and S. aureus. These data illustrate the polymicrobial nature and important role of BLPO in obstetric and gynecologic infection. 