Microradiography has been evaluated to measure bone healing into a 5.0 mm outer diameter mandibular defect in the rat. This method provides highresolution radiographs of the defects that can be used for an accurate measurement of bone defect healing. In 12 rats, the defect widths of 42-day-old mandibular defects have been measured both using microradiographs and histological sections. The defect width S:D: measured 3:42 0:98 mm microradiographically and 3:47 1:11 mm histologically. Both methods were accurate in determining defect widths but microradiography has the advantage over histology that an image is obtained from the entire defect, making it possible to measure areas of bone growth.