Abstract: An assay for directly and rapidly determining the alcohol concentration of a lower alcohol in a biological fluid without dilution, comprises a solid carrier. The carrier is impregnated with a solution having the following constituents mixed in effective amounts: a cross-linked stabilized enzyme for oxidizing the alcohol in the presence of a reducible compound to produce a corresponding aldehyde and a reduction product, a chromogen which reacts with the reduction product in the presence of an agent to produce a colored compound indicative of alcohol presence in the biological fluid, a competitive inhibitor of the enzyme, an agent for converting the chromogen to the colored compound, and a buffer to maintain the solution at a predetermined acidic pH.