Cellulase production was investigated in a culture of a strain of Acremonium cellulolyticus. The medium components were optimized for the improvement of cellulase production. The maximum production of cellulolytic enzymes was obtained in a medium containing (grams per liter) 50 Solka Floc, 5 (NH4)(2)SO4, 24 KH2PO4, 4.7 potassium tartrate hemihydrate, 1.2 MgSO4 center dot 7H(2)O, 1 Tween 80, 4 urea, 0.01 ZnSO4 center dot 7H(2)O, 0.01 MnSO4 center dot 6H(2)O, and 0.01 CuSO4 center dot 7H(2)O, with a pH of 4.0. In the flask culture, 15.5 filter paper units (FPU)/mL of maximum cellulase activity was obtained, 17.42 FPU/mL in a 7-L bioreactor, and 13.08 FPU/mL in a 50-L scale bioreactor for 4-8 d at 30 degrees C. Average production rates were 1.94 FPU/mL center dot d in flasks, 2.86 FPU/mL center dot d in the 7-L bioreactor, and 2.56 FPU/mL center dot d in the 50-L bioreactor. Cellulase production on a small scale was successfully reproduced in the 50-L pilot scale bioreactor. Saccharification activity from A. cellulolyticus was compared with cellulolytic enzymes produced by other strains. The A. cellulolyticus culture broth had a comparable saccharification yield in comparison with those of other Trichoderma enzymes (GC220 or Cellulosin T2) under the same total cellulase activity. Its saccharification yield (percent of released reducing sugar to used dried substrate) was 60%, and its glucose content was 83%.