There is increasing evidence that overheating is a contributing factor for some cot deaths. One hypothesis is that infant thermoregulation is closely related to respiratory control. To test this hypothesis it was necessary to determine the normal pattern of body temperature in the developing infant. A system has been designed and built to record continuously temperature signals from ambient, rectal, and various skin site sensors. Overnight studies were performed on 30 infants aged between 2 and 26 weeks in a hospital ward. Various time and frequency domain analyses of the temperature data have been developed. Analysis of body temperature rhythms has confirmed patterns during sleep which mature with age. In addition a periodic oscillation of body temperature has been found with a cycle of approximately one hour. This oscillation may reflect sleep state and its further study may give an insight into control of infant thermoregulation and the integration of this control with that of breathing and the cardiovascular system.