In order to understand the clinical efficacy of cefteram pivoxil (CFTM) in the treatment of asymptomatic bacteriospermia, the following studies were performed. 1. Concentrations of CFTM in the semen after oral administration of 200 mg to normal healthy adults (n = 5) reached a maximum level of 0.66 +/- 0.04 microgram/ml in 5 hours after the administration, then decreased rapidly, and averaged 0.15 +/- 0.03 micrograms at 7 hours after administration. 2. Activities of CFTM, cefaclor (CCL) and lomefloxacin (LFLX) against bacteria which were detected in semen (n = 65) (11 aerobic bacterial strains and 48 anaerobic bacterial strains) were retrospectively studied. The study of activities of these 3 agents against anaerobic bacteria showed that CFTM tended to be more active than CCL, LFLX, and similar tendency was noted in LFLX more than CCL against Peptostreptococcus sp. When penetration of antibiotic agents into semen is considered, however, some anaerobic bacteria as well as some aerobic bacteria may not be eradicated or inhibited, hence farther studies are needed to facilitate the selection of proper methods of administration as well as that of effective antibiotics.