The author studied the effect of periapical bone loss on radiographic interpretation by using a dry adult human mandible. Artificial bony lesions were created at the apices of two mandibular second molars and four mandibular bicuspids. The jaw was stabilized and various artificial lesions were radiographed under ideal circumstances. Radiographic pictures were recorded and compared with the size of the actual lesions. The obtained results were as follows: 1. The size of actual lesions were always larger than their radiographic pictures. 2. The size of actual lesion had a greater discrepancy in the molar area where the cortical plates were havier, but the lesions in the bicuspid areas were only slightely larger than their radiographic pictures, and in these areas the cortical plates were quite thin. 3 Periapical lesions located in cancellous bone did not appear on a radiograph, regardless of the size of the created lesion, but when the junctional bone was involved or the cortical plate was perforated, the definite bone destructive change was observed on the roentenogram. 4. Removal of the entire buccal or lingual plate did not affect the trabecular pattern of bone on the roentgenogram. 5. When the cancellous bone and junctional bone were removed simultaneously, altered trabecular patterns were observed on the roentgenogram.