One hundred fifty-two women who received cefazolin prophylaxis and subsequently developed postpartum endometritis were randomized to treatment with either ticarcillin/clavulanic acid (75) or clindamycin-gentamicin (77). Bacteria isolated from the endometrium were predominantly facultative anaerobic bacteria. The ratio of facultative anaerobes to obligate anaerobes was 3:1. Nineteen percent of the women were bacteremic, with mycoplasma the organism most frequently isolated from venous blood specimens. Cure rates were similar for both groups: ticarcillin/clavulanic acid 85% and clindamycin-gentamicin 81%. The advantages of ticarcillin/clavulanic acid are an increased spectrum of activity against beta-lactamase-producing bacteria, less toxicity, and lower cost.