Abstract: Mixtures of cationic thiazine dyes containing two or more members of the group consisting of thionine, azure A, azure B, azure C, and methylene blue may be resolved into pure individual compounds by column chromatography on slica gel using as a solvent system a mixture of water, acetic acid, and formic acid. The several fractions eluted sequentially from the column contain the pure individual dyes in the formate or acetate form. Because high solubility is essential for use of the dyes in staining blood smears, the acetates or formates are converted to the chlorides by adsorption on a solid substrate and contact with NaCl solution, elution with methanol, and recovery of the solid chlorides from the methanol solution.