The objective of this research was to test whether the udder skin temperature of a cow is useful as a heat stress indicator. Heat stress leads to an increase in respiration rate, skin temperature, and rectal temperature, followed by a decrease in milk production and feed consumption. Rectal temperature is a reliable indicator of heat stress, but measuring rectal temperature may require restraint of the animal. Skin temperature is considered a less reliable indicator of heat stress, but skin temperature measurements are fast and non-invasive. For this research, 8 primiparous, mid-lactation Holstein cows producing 34.4 ± 3.7 kg/d of milk were housed in 2 identical climate-controlled rooms with tie stalls and exposed to moderate heat stress (THI 79.5 ± 1.2) for 8 h per day. Cows were given 1 week to adjust to the facility, then data was collected for 5 weeks on milk production, feed consumption, rectal temperature, respiration rate, udder skin temperature, and body surface temperature in 3 unshaved locations (neck, back and side). Cows were milked twice daily and fed ad libitum. Rectal temperature was measured twice each day before heat stress conditions and after 8 h of heat stress. Respiration rate, udder skin temperature, and body surface temperatures were measured before heat stress and every 2 h during heat stress. Four experimental cows were randomly assigned to be cooled with conductive cooling by circulating chilled water through modified DCC waterbeds, and these cows experienced less heat stress than control cows. For the final week of the experiment, experimental and control cows were switched. Correlations among daily milk production and feed consumption, rectal temperature at the end of heat stress, and the daily average under heat stress of respiration rate, udder skin temperature, and body surface temperature were analyzed in JMP. Correlation with milk production was strongest for rectal temperature (0.67), followed by feed consumption (0.58), udder skin temperature (0.53), respiration rate (0.38), and body surface temperature (0.23). Thus, udder skin temperature may be useful as a fast, non-invasive measurement of heat stress.