Cultivation of three strains of Trichoderma reesei was performed in the presence of
cellulose and casein. Maximum enzymatic activities of cellulases were estimated during the cultivation of all strains in the presence of cellulose as the source of carbon. The highest secretion of proteases was observed during the cultivation of strains with addition of casein to the medium. The proteases present in the culture fluids of T. reesei strongly affected cellulases activities. Current knowledge about the correlation between proteases and other enzymes is presented in the paper. This work is an introduction for future studies on the correlation between proteases and other enzymes in culture filtrates of Trichoderma reesei.