The paper presented is dedicated to investigation of the temperature-humidity index (THI) and its impacts on the performance parameters of dairy cattle. These parameters were recorded at four farms in the central Slovakia; the experiments took place three years. These parameters comprised milking time, time spent in the milking box, and connection time. The THI was calculated according to the standard formula and individual periods were established on the basis of achieved THI values.The results showed that the milking time and the time spent in the milking box were not reduced when the THI ranged from 68 to 71, with a daily milk yield of 28.96 kg. If the THI exceeded 72, the milking time and the time spent in the milking box were shortened, which was statistically confirmed. However, even with a daily milkyield of 31.27 kg, a reduction in the milking time and time spent in the milking box was reduced. This was caused by the THI higher than 68, which was also statistically confirmed. Based on the results obtained, the dairy cows respond to heat stress by reducing the milking time and reducing time spent in the milking box.