The organophosphorus insecticide Selecron [O-(4-bromo-2-chlorophenyl) O-ethyl S-n-propyl-phosphorotioate] at 10 and 50 ppm significantly decreased respiration, mycelial protein, extracellular protein and mycelial dry weight of Aspergillus fumigatus, A. terreus and Myceliophthora thermophila when grown at 45°C. Cx and C1 cellulases of tested fungi were significantly decreased. However, C1 cellulase of A. fumigatus was slightly increased.