The decolourisation of Orange II by a wood-rotting fungus has been studied. It was found that Fungus F29 could effectively decolourise Orange II especially when grown as pelleted mycelia under agitated conditions. Many factors affecting the decolourisation process in nitrogen-limited media (NLM) were studied, including : concentration of glucose, NH4+, Mn(II) and veratryl alcohol; initial pH; amount of mycelium; mycelial age; Orange II concentration; temperature. Results showed that the media containing Orange II at 1000 mg dm(-3) (or higher) could be decolourised by 98% of the initial colour (A(480 nm)) in 2 days, in most conditions tested, and that the mycelia could be repeatedly reused.