The oxidative coupling reaction of 3-methylbenzothiazolone hydrazone with aromatic amines was applied to the determination of five 1,4-benzodiazepine derivatives. The drugs were first hydrolyzed in acid medium and the liberated benzophenone derivatives were reacted with the chromogenic reagent in the presence of cerric ammonium sulphate to give a pink color. A linear correlation was found between the absorbance at λmax and concentration. The method was applied to the determination of these drugs in bulk powder and in pharmaceutical preparations. The procedure was extended to develop a stability-indicating method for these drugs.