After intravaginal administration of a spermicide, nonoxynol (polyoxyethylene nonylphenyl ether, NPE) in female rabbits, the pharmacokinetics of NPE were examined by the HPLC method. The plasma levels after administration of NPE revealed a considerable amount of absorption of NPE into the circulation and the bioavailability after intravaginal administration was calculated to be 66% by comparison with that after intravenous administration. Unchanged NPE was not excreted into the urine in significant amounts even on intravenous administration. Nonylphenol (NP), a presumed metabolite of NPE, was simultaneously analyzed using GC-MS to assess the risk by its endocrine disrupting effects. Although the NP concentrations in the plasma were all below the lower limit of quantitation (10 ng/ml), small amounts of NP and its glucuronide conjugate were detected in the urine after intravaginal administration of NPE. Thus it was suggested that at least part of NPE absorbed in the circulation was metabolized to give NP. However, the sum of NP and its conjugate excreted in the urine was very small amounts (0.22% of dose). Therefore, it was assumed that the production of NP was not in the major pathway of the NPE metabolism.