Pharmacokinetic and clinical studies on cefotiam (CTM) in the perinatal period were performed and results obtained are summarized below. Concentrations of CTM in maternal serum, umbilical cord serum and amniotic fluid were examined after a bolus intravenous administration at a dose of 1 g. Data were analyzed using simulation curves drawn by the two- or three-compartment open model. The peak level of CTM in maternal serum was 86.6 micrograms/ml and the half-life of the beta-phase was 0.91 hour. Peak levels of CTM in umbilical cord serum and amniotic fluid were 20.8 micrograms/ml at 0.1 hour and 9.2 micrograms/ml at 3.2 hours after the administration, respectively. The concentration of CTM in amniotic fluid decreased after reaching the peak, but it was still as high as 1.6 micrograms/ml even at 12.0 hours after the administration. These results clearly demonstrated that the transfer of CTM to umbilical cord serum and to amniotic fluid was efficient in protection of perinatal infections. In a clinical trial, CTM was given to 11 patients with perinatal infections. Clinical efficacies were evaluated as excellent in 2 patients, good in 8 patients and poor in 1 patient. No adverse effects were observed in any of the patients studied. In conclusion, CTM was useful and safe antibiotic for the treatment of infections in the perinatal period.