Addition of bromothymol blue to quinine produces a color which is extractable with benzene. The method is applicable to blood, biol. fluids and tissues. Colors are also obtained with ephedrine, atropine, eserine, and strychnine. Cysteine, p-aminobenzoic acid, histamine, urea, adrenalin, caffeine, morphine, nicotine, sulfanilamide, aspirin, and glucose produced no extractable color. The method is sensitive to 0.25 [gamma] of alkaloid.