Polymicrobial infections with aerobes and anaerobes are common in female genital tract infections. We evaluated the efficacy of an injectable new quinolon, pazufloxacin, using a uterine endometritis model. Rats were infected with a mixed inoculation of Escherichia coli plus Bacteriodes fragilis (MIC of pazufloxacin and ceftazidime: E. coli: 0.05 and 1.56 micrograms/ml, respectively, B. fragilis: 3.13 and 3.13 micrograms/ml, respectively). After inoculating 10(7) cfu/rat of each organism, pazufloxacin or ceftazidime (10 or 20 mg/kg, respectively, i.v., b.i.d., 3 days) was administered and compared with the nontreated group. The viable cell counts of the uterine corpus and uterine cervix in pazufloxacin-treated and ceftazidime-treated groups were decreased, compared with the nontreated group. The viable cell counts of the adnexa in the pazufloxacin-treated group were significantly decreased, compared with the ceftazidimetreated group. These results suggest that pazufloxacin would be useful for the treatment of polymicrobial infections, especially adnexitis.