The transfer across the placenta and the maternal and neonatal kinetics of oxazepam and its conjugate was studied in 12 patients and their newborns. Oxazepam was readily absorbed and peak plasma concentrations were similar to those in healthy non-pregnant volunteers. When meperidine was given within one hour of the dose of oxazepam the absorption was delayed but the bioavailability did not decrease. In the newborns the umbilical vein plasma concentration of oxazepam usually exceeded that of the conjugate. The reverse was true for all subsequent plasma samples from the newborn. The half-life of oxazepam in the newborn averaged 22 hours as compared to 6.5 hours in the mothers. A significant rise of the plasma concentration of oxazepam conjugate was noted in three newborns during the first 6-10 hours of extrauterine life. This shows that the newborn is able to conjugate oxazepam. The Apgar score values were normal.