[en] A spectrophotometric study of the extraction with isobutanol of rare-earth elements in the form of complexes with quinoilizarin and N-benzene-N-phenylhydroxylamine has been made. The purpose of the study is to find out whether this reaction can be used in determining the concentration of elements in the presence of other rare-earth elements. In determining the relationship between the pH and light absorption the pH of the solution is measured after the extraction. The extraction of complexes begins at pH approximately 4 and reaches a maximum at pH7-8 (for La) and pH6-9 (for Er). The complexes underge decomposition when pH of the solution increased. The composition of complex compounds is determined by spectrophotometric methods for isomolar series, molar ratios and from the slope of logarithmic plots. Under optimal conditions (pH7.5) aAd at the measured ratio of the component for each ion of rare-earth elements, the molar extinction coefficients are determined for complexes in isobutanol solutions. Since the coefficients have approximately the same value, 1.2x10⁴ -1.8x10⁴ (La-Lu, Y) it is difficult to make direct determination of individual rare-earth elements in their mixture. On washing the extracts with a solution of sodium salicylate the elements of yttrium subgroup remain practically undecomposed. The elements of cerium subgroup under go decomposition in various degrees. Thus it is possible to determine any element of yttrium subgroup in the mixture with lanthanum; in particular in the determination of terbium mixed with lanthanum the sensitivity of the analysis is approximately 2% Tb₄O₇. The results of the analysis and the statistical treatment of the results are presented