In the literature, there are many studies on greenhouse gas and ammonia emissions from dairy barns, however their values are varied. The national inventory of gaseous air pollutants is performed by using theoretical standard emission factors according to the international methodology: Intergovernmental Panel on Climate Change (IPCC) and European Monitoring and Evaluation Programme (EMEP). The aim of the study was to determine the values of greenhouse gases (CH₄, N₂O) and ammonia emission factors during pilot research in commercial barns. The study was conducted in six livestock buildings for dairy cows located in the Wielkopolska Voivodship. The studied barns differed in a construction, the type of resting area and the manure removal system. The 18 daily measurements were made, the 3 test series in each barn. The mean calculated values of greenhouse gases and ammonia emission factors were: 135±47 kg·yr^-1·cow^-1 (103.4±35.9 kg·yr^-1·LU^-1) for CH₄, 0.91±0.74 kg·yr^-1·cow^-1 (0.70±0.57 kg·yr^-1·LU^-1) for N₂O and 8.9±5.2 kg·yr^-1·cow^-1 (6.9±3.9 kg·yr^-1·LU^-1) for NH₃ The converted on 1 LU (livestock unit = 500 kg), CH₄, N₂O and NH₃ emission factors differed from factors used by National Centre for Emission Management in 2013. The determined factors in this study were lower about 20% for CH₄, higher about 21% for N₂O and lower about 67% for NH₃.