Abstract: The present invention is an improvement in a method using a reporter dehydrogenase for detecting the presence of an analyte in a sample in which endogenous dehydrogenases present in the sample interfere with the detection of the analyte. The improvement is the inclusion of an inhibitor of the endogenous dehydrogenase in the assay medium. The improvement finds particular utility in the measurement of ethyl alcohol using alcohol dehydrogenase as the reporter enzyme when lactate and lactate dehydrogenase present in the sample interfere with the detection of the analyte. Particulary effective inhibitors which prevent this interference are fatty acids, such as, agaric acid and lauric acid, and alkyl sulfate salts, such as, sodium dodecyl sulfate and sodium decyl sulfate.