From the third to the sixth day postpartum transcervical endometrial swabs were taken from 51 women with the clinical signs of endometritis, like fever over 38 degree C, uterine tenderness and purulent lochia using prereduced anaerobic transport-media. The specimens were cultured aerobically and anaerobically. 27 women had an endometritis following vaginal delivery, 24 following caesarian section. Following vaginal delivery aerobic bacteria were isolated in 85.2% of the cases and anaerobic bacteria in 62.9%, post caesarian section in 75.1% aerobic and in 83.3% anaerobic bacteria. A mixed aerobic/anaerobic infection was found in 48.1% following vaginal delivery and in 58.4% post caesarian section. The aerobes most frequently recovered were Staphylococcus epidermidis, E. coli, Enterocococci and Streptococci, the prevalent anaerobes were the grampositive anaerobic cocci, Peptostreptococcus and Peptococcus, and Bacteroides species. Our results suggest that anaerobic bacterial play an important role in the endometritis post partum and that frequently a polymicrobial aerobic/anaerobic infection is present. Therapeutically, anaerobes should be taken into consideration especially for the treatment of severer infections following caesarian section. In such cases the 5-Nitroimidazoles, such as Metronidazole or antibiotics effective against anaerobes as Clindamycin or Cefoxitin should be administered.