Though the two-wavelength spectrophotometric determination1without the function generator permitted measurement of one component contained in two-component mixtures without sample pretreatment, it required proper wavelength selection and could not analyze some kinds of samples. The method of two-wavelength spectrophotometric determination with the function generator herein reported has succeeded in eliminating these limitations thus permitting the analysis of many kinds of samples. This method has further made it possible to measure one component contained in three-component mixtures.