The aim of the present study was to evaluate the degree of microbial air contamination in three laboratory rooms designed for raising broiler chickens under identical conditions, in the summer and winter. It was found that in identical poultry houses and under identical management conditions, certain differences can be observed with regard to temperature and humidity parameters and the degree of microbial air contamination, both in the summer and winter. The concentrations of aerobic mesophilic bacteria and fungi were higher in the winter than in the summer in all rooms. Various levels of microbial air contamination had no effect on broiler production results.