Holstein Friesian and Brown Swiss cows were kept in different ventilation conditions. Respiration, pulse rates of animals and daily milk yield, some milk components were investigated in optimal, unventilated and open shed barns. In unventilated barn physiological traits of cows were affected considerably. Barn II had delayed effect on daily milk yield and milk fat of cows after they were transferred to open shed barn. Also, lower temperature in barn III had negative impact on daily milk yield. Milk dry matter and pH were not influenced by barn ventilation. It is thought to be the primer step to attach importance to the barn ventilation, especially in cold climates.