The work deals in greater detail and more systematically than a previous study with several microclimate factors of the widely used today 100-liter inoculation cages; the effect of these factors can to one degree or another affect the results of the experiment. One of the basic life products of animals in inoculation cages is ammonia. Therefore, the authors considered it important as an indication of the degree of air contamination by volatile life products of the animals in the cages. These products include oxygen and carbon dioxide, ammonia, hydrogen sulfide, methane, indole, skatole, amines, amides, aldehydes and ketones, mercaptans, disulfides and other compounds. Concentrations of these products in the air depend on the kind of animal, the number per unit of floor area and the frequency of air exchange, as well on the kind of bedding material.