Temperature measurements have been made in cortical bone while drilling under controlled laboratory conditions. Cortical temperatures greater than 100 degrees centigrade were frequently recorded when drilling if no specific provisions for cooling were made. The force applied to the drill was found to be much more important than drilling speed as a factor in both the magnitude and duration of cortical temperature elevations. Increases in the force applied to the drill were associated with decreases in the maximum temperatures and the durations of temperature elevation. Worn drills caused much greater temperature changes than new drills. All forms of irrigation that allowed the stream of irrigating fluid to be directed to the point of penetration of the cortex were effective in limiting the increases in cortical temperature. Tapping did not appear to cause significant temperature elevations.