The influence of different parameters on the sporulation of Metarhizium flavoviride was studied during submerged cultures in shake flasks and in 51 bioreactors. The screening in shake flasks of several carbon and nitrogen sources allowed the definition of an optimal medium, based on sucrose and brewer's yeast with a C/N ratio of 1.6. With this medium, a production of 5.4 x 10(8) blastospores per ml (Bspores ml(-1)) was obtained after 169 h of cultivation. The influence of pH and pO(2) was independently studied in 51 working volume bioreactors using the optimal medium. The best production was obtained with pH and pO(2) regulated respectively to 7 and 100%. Finally, when the culture was grown under optimized conditions, the blastospores concentration increased 16-fold, with 1.1 x 10(9) Bspores ml(-1) obtained after 144 h cultivation. This represents a gain of productivity of about 4.8 times. (C) 2004 Elsevier Ltd. All rights reserved.