Phlebia gigantea is an aggressive white rot fungus that colonizes conifer wood. The influence of different carbohydrates: glucose, xylose, carboxymethyl cellulose (CMC), microcrystalline cellulose (avicel) and cellobiose were evaluated as carbon sources for the production of cellulase by this saprophytic fungus. Carboxymethyl cellulose gave the highest yield, followed by cellobiose and avicel. Glucose and xylose did not produce any detectable cellulases which suggest the repression of cellulase in presence of these simple carbohydrates by P. gigantea. These results showed that the production of cellulase not only depends on the pH but also on the consumption of carbon sources in medium. The higher yield of cellulase in presence of CMC, the amorphous cellulose, and less in presence of cellobiose the soluble intermediate product of cellulose hydrolysis, indicates the requirement of crystallinity and complexity for the higher yield of cellulase by P. gigantea. (C) 2006 Elsevier Inc. All rights reserved.