An investigation was made to evaluate currently used subtraction radiography techniques. The first order subtraction technique was found to be adequate for conventional clinical use. However when using fine-grain high contrast films for the originals, the second order technique gave a more accurate subtraction image. The limiting factor in the sensitivity of the radiographic subtraction technique for detecting small contrast changes over an area of about 2 cm in diameter was found to be film noise and not quantum statistics. Extra-fine-grain films were compared with conventionally used films. While these extra-fine-grain films gave slightly better results, they also required x-ray exposures which would be too high for routine clinical use.