Aspergillus awamori is an interesting fungus for the industrial production of enzymes. To generate essential information, fermentations with this organism (CBS 115.52) were performed under various conditions. The ratio of the biomass production to the sum of biomass production and carbon dioxide production in rime is used for deriving the yield and maintenance coefficient. This ratio can be used to estimate the biomass concentration from the CO2 production on line as well. Pellets were the dominant morphology for most of the fermentations performed. The hairy length of the pellets first increased with time and then decreased At a comparable specific energy dissipation rate, in the larger scale fermenters, pellets had a larger hairy length than in the smaller : The fraction of pellet biomass in the total biomass decreased with time at the beginning of the fermentations (0-20 h) and then reached a more or less stable value. Both counting the number of pellets during the fermentations and observing pellets under agitated but nongrowth conditions indicated that formation and breakage of pellets hardly occurred under the studied conditions.