Covalent immobilization of Trichosporon cutaneum R57 cells was conducted onto PA and PAN membranes with glutaraldehyde as a coupling agent. Amount of immobilized cells was determined: for polyamide - 1.4 mg cm(-2) and for polyacrylonitrile - 1.8 mg cm(-2) (dry weight). The efficiency of each immobilized system was evaluated by the extent of phenol biodegradation (1.0 g l(-1)). Polyacrylonitrile-immobilized system completed the process for 45 h, whereas polyamide-immobilized system for 51 h. During the six next cycles the complete biodegradation time for polyacrylonitrile-immobilized system was reduced at 24, 18 and 15 h for 111, V, VII cycles, respectively. The biodegradation time at eighth cycle was prolonged (42 h) and this is probably due to substrate diffusion limitations to the local accumulation of microbial cells on the membrane surface and cause cell death. Comparing the SEM of immobilized microbial cells on polyacrylonitrile membrane before the first cycle and after the eight cycle could be seen that great amount of immobilized cells are accumulated on the membrane surface during the seven biodegradation cycles. (c) 2006 Elsevier Ltd. All rights reserved.