The pharmacokinetics of triclosan was studied in sexually mature virgin Wistar rats. 14C-triclosan was injected either via the femoral vein, (iv, 5 mg/kg in polyethylene glycol-400) or into the vaginal orifice (ivg, 5 mg/kg in corn oil). Radioactivity was determined by liquid scintillation spectrophotometry. After iv administration, the dissapearance of 14C from the blood followed the kinetics of a two-compartment open-system model. The apparent volume of distribution was 42 percent of the body weight, which is more than the extracellular water, suggesting a rapid transfer of this antimicrobial agent from plasma to tissues. The blood half-life of 14C during the beta-phase was 8.8 +/- 0.6 hr and the blood clearance rate was 77.5 +/- 11.3 ml/kg/hr. After ivg administration of 14C-triclosan, the radioactivity was detected in tail blood at 15 min, peaked between 2 to 4 hr, and declined rapidly to 6 hr more slowly thereafter. About 26 percent of the administered dose remained in the vagina after 4 hr and 12 percent after 24 hr. Tissue concentrations of 14C were highest in the plasma, kidney, and liver after ivg application, but extremely low in the brain, fat, and skeletal muscle. The percentages of the dose excreted in 24 hr in the feces and urine were 18 and 9 after iv administration, compared to 26 and 14 after the ivg route, respectively. The results show that triclosan is rapidly absorbed through the vaginal mucosa of the rat.