Tympanic temperature was monitored during labour and delivery in six primigravidae and five multigravidae. Temperature increased temporarily with each contraction and progressively during the course of labour. The increases, which were greater in primiparae than in multiparae (mean cumulative increase 1.46 degrees C and 0.51 degress C respectively), reflect the metabolic expenditures associated with contraction of uterine and skeletal muscles.