Abstract An investigation is described of the drilling process in bone. Experimental results are presented which show the interrelationships among thrust pressure, feed rate, torque, and specific cutting energy for three types of drill bits. The three types of drill bits used included a common surgical twist bit, general purpose twist bits of various diameters of the type normally used for drilling into metals, and a specially constructed spade bit. It is shown that the performance of all three types of drill bits can be characterized by power function relationships of the same form. Clogging of drill flutes is identified as a serious problem which causes increased torque and energy as the drill bit penetrates deeper into the bone. Optical and scanning microscopy of drilling chips indicate that chip formation occurs primarily by a fracture process with localized deformation resulting from the action of the chisel edge at the tip of the drill bit.