A simple and practical biological process for the decolorization of coloured effluent from a textile company is described. A number of aerobic and anaerobic cultures able to decolorize dyes in textile effluent samples were isolated after prolonged enrichment culture from textile dyes-effluent samples. The decolorization of some component dyes of the effluent and of a mixture of dyes was achieved under anaerobic conditions, indicating that the bacteria were able to break the chromophoric bonds in the dye molecules. Several bacterial cultures capable of total decolorization of some effluent component dyes under anaerobic liquid fermentation conditions were isolated. One of the cultures decolorized Cibacron Red (reactive dye), Remazol Golden Yellow (azo dye) and Remazol Red (diazo dye) completely within 24-30 h fermentation process; Remazol Navy Blue (diazo dye) and Cibacron Orange (reactive dye) within 48 h; and Remazol Blue within 54 h. These decolorizations were permanent with no colour change upon exposure to ail : Only one dye, Remazol Turquoise Blue (a phthalocynaine dye), was partially reversibly decolorized. Potential applications of the cultures obtained in textile dye stuff effluent decolorization and treatment are discussed.