Many basidiomycetes, especially mushroom species, thrive on saccharides that they obtain from the decomposition of cellulose, hemi-cellulose and or lignin. Cellulose is degraded by specific enzymes called cellulases. Cellulases play an important role in the biosphere by recycling cellulose, the most abundant carbohydrate produced by plants. Also cellulases have many potential biotechnologic and industrial applications. Detection of cellulose degrading activity is commonly performed on carboxymethylcellulose CMC medium in combination with a stain that reveals the degraded CMC. In order to efficiently screen the F. velutipes knockout library, obtained through Agrobacterium-mediated transformation (ATMT), for those important enzymes we compared two different staining methods i.e. Congo Red and Gram’s Iodine (as reported in R. C. Kasana et al 2008). The latter stain showed strongly enhanced detection in time and intensity, facilitating mass screening of our mutant database. Using Gram’s iodine and square petri dishes containing up to 9 colonies at a time we can now rapidly screen multiple mutants in a short period. We are going to find the genes. Inactivated genes of mutants with altered cellulase degradation activity will be identified and cloned for further analysis.