A wide range of strains of white rot fungi have been shown to be effective in the decolourisation of a chemical industry effluent containing a diazo-linked chromophore. The five most effective strains were selected for further study, all could give ca. 70-80% decolourisation. Of these the best were strains of Coriolus versicolor. All five strains could decolourise the effluent at 5-40% v/v in nitrogen-limited medium. The greatest % decolourisation occurred at low effluent concentration but the initial rate and final extent of decolorisation was greatest at 40% v/v. At best, colour reductions of 119 and 147 absorbance units (at λ m a x ) were achieved in 3 and 7days, respectively. The presence of added manganese ions did not affect decolourisation although it did stimulate production of a red side product by some fungi. These results demonstrate the potential of white rot fungi in the treatment of chemical industry wastes.