Abstract: A method of discriminating alcohols different from ethanol in breath samples includes sampling voltages from a fuel cell at a rapid rate to establish a curve rising, upon introduction of a sample containing a known amount of ethanol without interferants, from an initial base line to a peak; determining a peak voltage; establishing an end point; determining the area under the curve from the introduction of the sample to the end point, and determing at least two other areas under the curve between the peak and the end point, a peak area, between the peak and a point on the curve relatively near the peak, and a trail area, between the end point and a point nearer the end point than the peak area; introducing to the fuel cell a breath sample that may contain an interferant in the form of an alcohol different from ethanol, and determining the peak voltage, end point, total area, peak area and trail area using the same criteria as were used in determining those pieces of information in connection with the sample co