Fifty-four tumors or tumor-like conditions in bone were studied by numerically assessed 99m-technetium polyphosphate scintigraphy. The uptake was expressed as a ratio of the uptake in the tumor region to the uptake in a corresponding region in the contralateral part of the body. In the malignant tumors there was marked variation in the uptake within each individual tumor group, a variation that rendered a differential diagnosis impossible. In general, the uptake was fairly high in malignant tumors and lower in benign ones. A ratio below 1.5 suggested the likelihood that the lesion was benign. The ratios also varied considerably with the site of the tumor and the patients' ages. Relatively low ratios were found for tumors of the trunk and for juxta-articular tumors in children, whereas higher and more varied ratios were observed in tumors of the peripheral skeleton in adults. It is concluded that numerically assessed scintigraphy is not a useful supplement to other methods used for diagnosing bone tumors.