The method of quantitative spectrophotometric analysis of several substances in the presence of admixtures is described. The method is based on presentation of an unknown spectrum of the admixture absorption by the polyen of the 3rd or 4th power depending on the wave length. The optical density of the mixture of any wave length is expressed by the linear equation, including the Firord equation for the known components and the given polynome. The system of such equations for 10-15 analytical wave lengths may be solved with the method of the least squares using an electronic computer. The system solvations are the concentrations of the mixture components to be determined and the polynome coefficients. The method was tested on model mixtures composed of amphotercin B, myocheptin, nystatin and griseofulvin, as well as of isomeric nitroanilines playing the role of the admixture. The analysis error for the compounds of the polyenic structure having not less than 2 absorption maxima in the given spectral ranges did not exceed 1-3 per cent. As for the compounds with a single maximum or when the admixture included also polyenic compounds the analysis error increased up to 6--50 per cent.