The undulating area of the distal femoral physis has been measured in New Zealand White rabbits, by using an image analyzer in histologic sections, and correlated to radiographic measurements. The relative size of a physeal drill injury necessary to cause growth disturbance has been found to be 7-9%. A transphyseally placed tendon, even as a free graft, prevented solid bone-bridge formation in the drill hole and growth disturbance. The results are of possible clinical significance.