Abstract: The application was studied of a detection cell with an enzyme immobilized on carbon fiber as an amperometric electrode in an organic flow stream. Peroxidase or monophenol monooxygenase was adsorbed onto the fiber to form the electrode which was operated with a Pt auxiliary electrode vs. Ag - AgCl as reference. The test analytes were 2-butanone peroxide, dodecanoyl peroxide and p-cresol and carrier electrolytes were 0.1 M tetraethylammonium p-toluenesulfonate in either CHCl3 saturated with phosphate buffer (pH 7.4) or aqueous 95% acetonitrile. Results obtained are presented and discussed and applications are proposed.