Pharmacokinetic studies and clinical evaluations of cefotiam (CTM) were carried out in perinatal mothers and infants and following results were obtained. The drug was promptly absorbed after intravenous injection or intravenous drip infusion in pregnant women, producing dose-related peak serum levels. Placental transfer to the fetus was effective. After intravenous injection or intravenous drip infusion of 1-2 g of CTM, drug concentration of the umbilical cord blood, amniotic fluid and fetal blood exceeded MICs of the drug against main pathogenic organisms. By administration of the dose of 1-2 g twice a day, therefore, perinatal infections should be successfully prevented or treated. Clinically, CTM was effective in the treatment of perinatal infections. Moreover, newborn infants delivered from mothers receiving CTM treatment had drug concentrations higher than MICs of CTM against main pathogenic organisms. Blood CTM concentrations in infants, however, did not remain high very long after birth, and these infants did not exhibit any abnormalities in laboratory tests. Penetration of CTM into mother's milk was ineffective, thus the transfer of CTM from milk to newborn infants was negligible. These results demonstrated that CTM is a clinically useful antibiotic for the prophylaxis and the treatment of perinatal infections.