It can be difficult to obtain reliable theological data for filamentous fermentation broths using conventional instruments. One common approach is to measure the torque drawn by an impeller rotating in the suspension (1-7). Many previous workers have assumed that the applicable shear rate in such a device is related to the impeller speed by a fluid-independent constant determined by calibration with Newtonian and non-Newtonian fluids (1-9). The theology of Aspergillus niger broths have been characterized using the impeller viscometer approach. The changes in the broth theology were measured, and used to interpret the growth of biomass and the evolution of the microorganism morphology.