For the industrial production of enzymes using fungi, often complex media containing solid substrates are used. in this study, fermentations with Aspergillus awamori were performed using wheat bran. The results are compared with previous work on synthetic medium. Major differences are that the wheat bran was not consumed completely as glucose or sucrose and that fungi growing on the wheat bran particles (adhesion growth) may occur depending on the inocula used. If the spore concentration was higher than 1.3 x 10(5) spores ml(-1), adhesion growth dominated. If the concentration was lower than 1.8 x 10(4) spores ml(-1), wheat bran free pellets and clean wheat bran particles dominated. In between these two values, the broth suspension consisted of wheat bran free pellets, clean wheat bran particles, and adhesion colonies. Solid substrate suppressed the growth in free filamentous mycelial form. A method was developed to separate rite wheat bran particles from the pellets. The kinetics with complex-medium appeared to be essentially the same as with synthetic medium. The ratio of biomass production to the sum of biomass production and CO2 production was a function of time and independent of operation conditions, morphology, and substrates (sucrose, glucose, or wheat bran). Gas-liquid mass transfer coefficients during the fermentations were determined and compared with a correlation from the literature.