A new method for quantitative determination of ethanol in blood described. A small amount of deproteinized whole blood (20 μl) is incubated with alcohol dehydrogenase and NAD in the presence of p-iodonitrotetrazolium violet (INT) and phenazine methosulfate. The reduced formazan is soluble and its absorption at 500 nm is proportional to the amount of ethanol which is present in the sample. The reaction is completed within 25 min and the chromogen is relatively stable. This method was compared to two other methods currently used: (a) the chemical method based on the reducing power of ethanol on the nitrochromic reagent; (b) the enzymatic method in which the generation of NADH is measured at 340 nm. The results show that the “INT method” is more specific and more accurate. Furthermore it is recommended for its speed and simplicity.