Two distinct forms of carboxymethylcellulase (CMCases) were produced by Paecilomyces sp. in a medium containing 5% (w/v) rice hull as the carbon source. CMCases I and II were purified 13.2- and 127.3-fold, respectively, by acetone precipitation, ion-exchange chromatography on DEAE-Sephadex A-50 and gel filtration on Sephadex G-200. Both enzymes were optimally active at 60 degrees C and retained 100% of their original activity at 50 degrees C for 2 h. They were also maximally active at pH 4.0 and stable between pH 4 and 5. CMCase I was activated by Ca2+, while CMCase II was activated by Ba2+. Both enzymes were, however; totally inhibited by Zn2+, Hg2+, glycine and EDTA. CMCase I and II had K-m values of 1.42 and 0.91%, respectively, for carboxy-methylcellulose. The relative molecular weights were 55 and 42 KDa for CMCases I and II, respectively.