Ceftriaxone (Ro13-9904, CTRX), a newly developed cephalosporin antibiotic, was fundamentally evaluated through determination of the levels in the female genital organ tissues and in the pelvic dead space exudate. CTRX was also studied on its clinical efficacy in 13 cases with gyneco-obstetric infections. The transmission of CTRX into the female genital organ tissues was favorable: the peak level in each tissue was as high as 38 to 63 micrograms/g 18 to 37 minutes after administration. The level in each tissue even after about 18 hours remained around 10 micrograms/g, suggesting its better transmission into the tissues than other drugs. The transmission into the pelvic dead space exudate was also good: the level reached a peak of 100 to 120 micrograms/ml 1 to 3 hours after administration and still ranged from 74 to 76 micrograms/ml even after about 12 hours. The clinical efficacy was excellent in 5, good in 5 and poor in 3 out of 13 cases with gyneco-obstetric infections and the efficacy rate was 76.9%. Neither adverse reaction nor laboratory test abnormality was observed in any case. The above-mentioned results suggest that CTRX is a useful antibiotic for gyneco-obstetric infections.