Electrical resistance rosette strain gauges bonded directly to the surface of the midshaft of the normal canine tibia were utilized to study the effect of the AO external skeletal fixator on the magnitude and orientation of the peak strain values recorded during locomotion. The application of the fixator in a single lateral bar configuration resulted in a significant decrease in surface bone strain magnitude but in only minor changes in the orientation of those strains. However, in only one of three dogs tested did the addition of a second external connecting bar result in significant further decreases in bone strain.