Abstract
Counts of microorganisms in the air of air-conditioned animal laboratories, carried out when the animals (rats, Chinese hamsters and rabbits) were quiet, revealed significant distribution patterns due to natural convection currents from the animals. The concentration of airborne microorganisms depended on animal activity, and soiling of bedding caused no increase. It was concluded that even in air-conditioned rooms random distribution of airborne microorganisms is unavoidable.