Pharmacokinetic and clinical studies on imipenem/cilastatin sodium (IPM/CS), a parenteral carbapenem antibiotic combination drug, were carried out in patients in the perinatal period. The obtained results are summarized as follows. 1. Concentrations of IPM and CS in umbilical cord blood, amniotic fluid and maternal blood were determined in 13 patients after 500 mg/500 mg of IPM/CS was administered by a drip infusion over a period of 30 minutes. Peak levels of both drugs in umbilical cord blood were about 30% of those in maternal blood. Although the levels gradually declined thereafter, the decline was slower in umbilical cord blood than in maternal blood and the levels became higher in the former than in the latter after 2 hours or more. The transfer of both drugs into amniotic fluid was slower than into umbilical cord blood. Peak levels were observed 5-6 hours after administration, averaging about 30% of that in the maternal blood for IPM and 45% for CS. 2. A 500 mg/500 mg dose of IPM/CS was administered to 10 patients with postpartum infections by a drip infusion over a period of 30 minutes or more twice daily in the morning and in the evening. Clinical responses were excellent in 6 patients and good in 4, with an efficacy rate of 100%. Bacteriologically, all of the 19 strains identified previous to the treatment were eradicated except for 1 strain. However, one new strain of Enterococcus sp. appeared in 1 patient. No side effects or abnormal laboratory findings were observed. These results suggest that IPM/CS will be useful for the treatment of various infections in the perinatal period.