The influence of the growth of two white-rot fungi, Pleurotus ostreatus and Lentinus edodes, on the composition and on the digestibility of com straw (Zea mais) was evaluated. P. ostreatus and L. edodes showed a different pattern of release of extracellular enzymes, including phenol-oxidases, cellulases and xylanases. The best results in terms of delignification and increase in digestibility were obtained in L. edodes cultures. When the two fungi were grown in submerged fermentation conditions in the presence of a water-soluble lignin-rich copolymer, a crude filtrate containing phenol-oxidases but no cellulolytic enzymes was obtained. Com straw, treated with the above mentioned crude filtrate and subjected to paper pulping, gave paper handsheets with improved technical properties (freeness, breaking length and burst index).