Aspergillus fumigatus was the most frequently isolated thermophilous fungus from green leaf surfaces. The application of fungicides significantly reduced the frequency of its occurrence there. A. fumigatus was relatively tolerant to fungicides. On Captan-, Thiram-, and Verdasan-treated leaves, A. fumigatus constituted 66%--80% of the total number of isolates obtained at 45 degrees C from each treatment while Dicloran did not depress the percentages. At 45 degrees C, A. fumigatus was found to be strongly cellulolytic with a slow rate of radial extension on YpSs agar and rapid rate of mycelial growth in Czapek Dox liquid medium. Increasing concentrations of all four fungicides reduced or prevented growth, sporulation, starch depletion and cellulose clearing of A. fumigatus. The fungus could tolerate higher concentrations of HgCl2 than of Verdasan. 2.5 microgram/ml of the four fungicides altered the rates of mycelial growth but not the maximum amount of mycelial dry weight attained.