Seventy boars penned singly in an artificial insemination station were included in this analysis. Each had a special ear tag with an integrated sensor to measure the skin temperature of the ear every 3 min. The readings were averaged per animal and hour, thus, over 18 months, resulted in a total of 37,7351 data points. In the whole investigation period, the system did not work for some days and some sensors did not work for hours. A diurnal rhythm was found for the ear temperature with its minimum reached between 5 and 6 am (22.07 degrees C) and the maximum between 4 and 6 pm (28.90 degrees C). If the ambient temperature was increased by 5 Kelvin then the skin temperature at the ear also increased by 3 to 5 Kelvin. On days when semen was collected, the ear temperature was higher during the relevant hours than at comparable times on days without semen collection. The results of 322 measurements taken from 70 boars, including 24 boars with increased rectal temperature (> 39.3 degrees C), showed that the coefficient of correlation between skin and rectal temperature was low (r = 0.36). Thus, the measurement of the skin temperature at the ear cannot be used as a significant or safe parameter for predicting the rectal temperature and sowith the health status of the animal.