Ninety two fungal species recovered on cellulose - CZAPEK's agar plates from Egyptian soils were assayed for their cellulolytic activities either at 28-degrees-C (mesophilic) or at 45-degrees-C (thermophilic or thermotolerant). The percentage increase of protein-nitrogen over those of control was taken as a measure of this ability. At 28-degrees-C, the top species in cellulolytic activity were Penicillium oxalicum, Nectria haematococca, Gliocladium catenulatum, Myrothecium verrucaria and Aspergillus niger. The other species showed low, weak or non cellulalytic activity. At 45-degrees-C, the highest activity was manifested by Chaetomium olivaceum, Sporotrichum thermophilum, Sepedonium chrysospermum, Aspergillus fumigatus, Humicola minima, Rhizomucor pusillus and Thermomyces lanuginosus. All penicillium species tested as well as some other fungal species were not capable of utilizing cellulose at 45-degrees-C.