Free-cell cultures of Trametes versicolor were compared with cultures immobilized on nylon mesh in a 2-litre bioreactor for transformation of pentachlorophenol (PCP) and 2,4-dichlorophenol (2,4-DCP), added at intervals to the liquid culture medium over a period of 816 hrs. Increasing amounts of PCP from 200 ppm to 2000 ppm added batchwise to cultures permitted acclimatization of the fungus to these toxic pollutants. A total addition of 2000 ppm of 2,4-DCP and 3400 ppm PCP were removed from the immobilized cultures with 85% of 2,4-DCP and 70% of PCP transformed by enzymes (laccase and Mn-peroxidase), 5% 2,4-DCP and 28% PCP adsorbed by the biomass and 10% 2,4-DCP and 2% PCP retained in the medium at the termination of the fermentation after 1020 hrs. In contrast free-cell cultures in the same medium with the same addition regime of PCP and 2,4-DCP, transformed 20% 2,4-DCP and 12% PCP by enzyme action, adsorbed 58% 2,4-DCP and 80% PCP by the biomass, and retained 22% 2,4-DCP and 8% PCP in the medium. The use of nylon mesh as an immobilization matrix for removal of PCP and 2,4-DCP facilitates more efficient removal of chlorophenols and can be adapted to scale-up for application of large volumes of chlorophenol-containing aqueous effluents.