A number of industrial processes require the addition of materials to the fermentation broth that are hazardous to health and environment. Agitation of broths inoculated with microorganisms can potentially release aerosols large enough to carry the microorganisms. The influence of agitation, air flow, and bacterial growth on aerosol size distribution, air flow, and bacterial growth on aerosol size distribution was investigated in an industrial pilot scale fermentor. A decrease in particle concentration was observed with increase in bacterial growth; this change was more pronounced in the size range above 2 μm. The aerosol size distribution was found to be practically independent of air flow rate and agitation rate for sizes less than 2 μm. However, for particles largar than 2 μm, the concentration was found to increase with an increase in air flow rate and agitation rate.