The objective of this study was to ascertain if regular cooling by sprinkling could influence the heat stress in high-yielding dairy cows and which of monitored parameters are suitable heat stress indicators. High ambient temperatures affected homeostasis in dairy cows. The heat stress increased respiratory and pulse rates and rectal temperature. Haemoconcentration also occurred, which was proved by haematocrit enhancement and increase in red blood cell number and total proteins in blood serum. As urea concentration increased, its monitoring could be a suitable parameter for heat stress intensity check. When the cows were cooled by sprinklers, only a mild growth of physiological and haematological parameters occurred. Evaporative cooling reduced heat stress, but it had only a small influence on metabolic symptoms at high temperatures. The changes were the most intensive in dairy cows with the highest milk yield and evaporative cooling had the best effect on them.