With the widespread use of AI on many commercial dairy farms, the efficient detection of oestrus has become a subject of increasing importance. Of all the physiological variables that have been investigated as predictors of oestrus, body temperature monitoring either on its own or in conjunction with other physiological variables, has shown promise mainly because of the ease with which it can be adapted as a practical on-farm oestrus detection system. However, oestrus detection rates by body temperature monitoring rarely exceed 70-80%, and often 10-20% of non-oestrus cows are wrongly diagnosed as being in heat. If the percentage of false positives is to be minimised, then identifying those factors that affect body temperature is important. Equally important, is an understanding of the way and the extent to which each factor affects body temperature. The more complete these two pieces of information, the more confident can one be of diagnosing an oestrus cow correctly. The aim of the present study was to investigate whether the behaviour of a dairy cow affects her body temperature, and what light this information can throw on the use of body temperature as a predictor of oestrus.