The partition of cellulase from Trichoderma viride in aqueous two-phase systems has been investigated with the purpose of designing a phase system for the bioconversion of cellulose. The partitioning of the enzyme in the two-phase systems composed of various water-soluble polymeric compounds, and the influence of polymer molecular mass on polymer concentration are studied. Systems based on dextran and polyethylene glycol (PEG) proved to be optimal for partitioning the enzyme to the bottom phase which is rich in dextran T500. Cellulases produced by Trichoderma vir ide grown on Solka-Floc BW200 were fractionated by ammonium sulphate (50%) and purified by chromatography on DEAE-Sephadex A50. The overall purification steps showed a protein reduction of 97% of the original protein content of the culture filtrate. On the other hand, the specific activity (FPU) was increased 24-fold. In optimization experiments, the maximum enzyme activity was found at pH 4.8 when incubated at 28 degreesC for 11 days.