The technique is based on the reaction of ethchlorvynol with diphenylalamine under acid conditions to produce a red chromophore. The intensity of the color, ranging from pink to rose-red, is dependent on the concentration of the ethchlorvynol. The rate of formation of the chromophore and the sensitivity of the test, however, are dependent on the acid conditions. In a sample volume of 200 microliters (ul), the methanolic precipitation of blood proteins and a final sulfuric acid content of 26 percent yielded color development within 5 minutes which was sensitive to the low therapeutic concentration of 5 micrograms/milliliter. The total time for processing the 200 ul methanolic extract from 1.5 milliliters of blood was 15 minutes. The method is also applicable to methanolic extracts of serum and tissue and can be performed semi-quantitatively with a series of standards. In contrast to existing methodology, the proposed method provides a rapid, sensitive, and specific screening test for this sedative- hypnotic agent in blood and tissue analysis. 1 figure and 22 references (Author abstract modified)