An investigation was carried out to determine the therapeutic effect of panipenem/betamipron (PAPM/BP), a injectable carbapenem antimicrobial agent, on infections in pregnant women during perinatal period. Of the 41 patients enrolled in the study, 34 were subjected to the analysis, with 1 exemption because of protocol violations (regimen), 3 because of uncertain evidence symptoms of infection, and 3 because of failure to undergo laboratory tests. PAPM/BP was administered by intravenous drip infusion at doses of 0.5 g twice or three times a day daily for periods of 3 to 14 days. The efficacy rate according to the evaluation of the Drug Efficacy Evaluation Committee and the attending physicians was 79.4% (27/34), with 49 of the 61 clinical isolates (80.3%) being eradicated. Safety was evaluated as "safe" in 39 of the 41 assessable patients (94.1%). Mild headache and nausea were experienced by 1 patient (2.4%) as adverse drug reactions, but the symptoms disappeared after the completion of treatment. Slight elevations of GOT, GPT and LDH in laboratory tests were observed in 1 patient (2.4%), but these values returned to normal after the completion of treatment. These results suggested that PAPM/BP may be a useful drug in the treatment of bacterial infections during the perinatal period. To firmly establish its safety, however, further clinical and pharmacokinetic studies are needed in larger populations.