□ A simple and specific method has been developed for determination of enviroxime in biological samples. Enviroxime, a substituted benzimidazole, its coisomer zinviroxime, and the internal standard hexestrol were extracted from the samples with benzene. The benzene layer was evaporated and the residue was reconstituted and injected onto a liquid chromatograph. Reversed-phase chromatography on an octylsilane column with a 65% methanol−35% 0.14M sodium acetate mobile phase separated the components. The compounds were detected electrochemically using a glassy carbon electrode held at +0.85V. The assay could detect as little as 4ng of enviroxime/ml of plasma, 15ng/ml of nasal wash, and 20ng/ml of urine or tissue homogenate. For plasma assays, the procedure was >97% accurate and had a relative standard deviation of <4%. This method has proven to be applicable and reliable for the determination of enviroxime in many types of biological samples. Several problems encountered during the routine use of electrochemical detection were explored and minimized.