A computerized technique for measuring total lung capacity from radiographic chest films based on methods originally suggested by Barnhard and associates has been developed. Total lung capacity is automatically determined by tracing the margins of the lungs in both posteroanterior and lateral radiographs with a commercially available hypersonic coordinate digitizer. The results compare favorably with those obtained using a body plethysmograph. This simple, automatic procedure requires minimal training, is rapid, and can be easily implemented.