The microclimate in livestock buildings is very important for health and welfare of farm animals, as well as for the efficiency of livestock production. The aim of the study was to evaluate the microclimate based on measurements of the selected parameters in a two-storey, fully-slatted piggery from July to October 2013. For five selected days, temperature and relative humidity inside the building, the concentration of NH3, CO2 and N2O and air exchange were recorded. The evaluation of temperature and humidity conditions showed that in the monitored piggery, pigs can be exposed to heat stress. The duration of adverse conditions can be as high as 80% of the day in the summer season. Mean daily NH3 concentrations ranged from 5.92 to 19.51 ppm, and were lower than the limit of 20 ppm. The analysis of the daily distribution of ammonia concentrations showed that in the autumn they were higher than the limit for 40% of the day. Daily average values of CO2 concentrations ranged from 1092 to 2407 ppm, and were lower than the limit of 3000 ppm. Average daily N2O concentrations ranged from 0.48 to 0.82 ppm, and did not negatively affect the comfort of the animals.