The absorption and excretion of sodium prasterone sulfate (PS) (sodium dehydroepiandrosterone sulfate) were studied in rats after vaginal administration of 14C-PS. In late pregnant rats, maximum plasma level (Cmax) appeared at 2-4 h after dosing and both Cmax and the area under the plasma concentration-time curve (AUC) increased proportionally with increased dose up to 4.0 mg/kg. The radioactivity administered was almost completely recovered from urine and feces during a 72 h postdosing period. The percentages of radioactivity excreted in urine and feces were 58% and 40% of the dose, respectively. The biliary excretion was 46% of the dose within 48 h and about half of the radioactive biliary excreta entered the enterohepatic circulation system. The vaginal absorption of PS was markedly affected by the estrous cycle stage and the progress of pregnancy. The vaginal absorption of PS was predominant at metestrus and diestrus and during late pregnancy.