The effects of environmental conditions on temperature rhythms were investigated in ewe lambs at pasture. Two groups of 20 lambs had heart rate (HR), vaginal temperature (Tv), ear-canal temperature (Tc) and ear-pinna temperature (Tp) monitored continuously for 3 days. Climatic conditions were recorded at the same time and Temperature Humidity Index (THI) calculated. One group experienced fine clear weather for the 3 days, the other group experienced 2 days of heavy rain. During periods of fine weather, the daily rhythm for Tv and Tc was monophasic. However, heavy rain and a constant THI reduced the amplitude of the recorded temperature rhythms. Daily Tv and Tc patterns correlated strongly with THI, with a phase lag of 2 h. Peak Tv and Tc were at approximately 17:00 h each day. Mean maximum daily amplitudes were approximately 1.3°C for Tv and Tc. Mean Tv was 39.3±0.1 and 39.6±0.1 for weeks 1 and 2, respectively, while mean Tc was 38.9±0.1 and 39.2±0.1. Changes in Tv and Tc were closely correlated. We conclude that climate has a major effect on body temperature rhythms.