14C-piperacillin (Pipracil) at a dose level of 1000 mg/kg was administered intravenously or intraperitoneally to pregnant and non-pregnant female rats. Rats were sacrificed at predetermined time intervals, and 14C-piperacillin concentrations determined in serum, amniotic fluid, placenta, and fetus. The piperacillin serum levels in both pregnant and nonpregnant rats following intravenous administration were comparable; however, following intraperitoneal administration, the serum drug levels in the pregnant rats as compared to the nonpregnant rats were lower. The fetal drug levels, however, were higher following intraperitoneal administration than following intravenous administration. The total area under the fetal drug concentration-time curve following intraperitoneal administration was about two times the corresponding area under the curve following intravenous administration. The data indicate that the fetal exposure to piperacillin was greater following intraperitoneal administration.