DIRECT azo dyes contain in most cases a number of coloured by-products which may adversely influence the shade of the dye, its stability in light and distort its biological action. In view of the importance of direct azo dyes in industry as well as in biology and medicine a number of authors1–10 worked on the problem of their purification. So far it has not been possible to separate these dyes completely (strong adsorption of dyes on cellulose in paper chromatography or electrophoresis, losses during crystallization, etc.). This communication describes a simple method of separation which excludes use of cellulose. Tests with agar electrophoresis, though there was some movement of dyes, did not lead to satisfactory separation. Therefore, I carried out adsorption chromatography on aluminium oxide. This method, though it has been frequently used for the separation of other dyes11–15, has not been used in practice for direct azo dyes.