Diel activity patterns of carabids species caught in pitfall traps in a subalpine birch forest north of the Arctic Circle are described. Patrobus assimilis Chaud. and Notiophilus aquaticus L. were the most common species and were active at all times of the day with peak activity at noon. Seven less common species and the larvae of Notiophilus aquaticus L. showed similar activity patterns. There was a positive correlation between the mean diel variation in temperature and the activity of the different species. Although day to day variations in temperature influenced the level of activity, it had little effect on the daily activity patterns. The adaptive significance of the diurnal activity patterns of carabid beetles in northern areas is discussed in relation to low night temperatures and high predation pressure from birds.