An amperometric biosensor for the determination of ethanol vapor has been successfully fabricated on a flexible polyester substrate using simple thick-film technology. Conventional screen-printing technology was employed to apply alcohol dehydrogenase to the carbon working electrode. For the activation, the sensor was either exposed to a humidified gas or prehydrated by dipping in a buffer solution. The latter method was found to be more effective than the former. A good linear response to ethanol vapor has been obtained. We have demonstrated that the amperometric thick-film biosensor can satisfactorily be used for the disposable determination of breath alcohol.