Bone to soft tissue (ST) ratios for both high-uptake bone (sacrum) and low-uptake bone (femoral diaphysis) were obtained with a derivative of phosphonic acid, TC-99m 2,3-dicarboxypropane-1, 1-diphosphonate (DPD), in 26 normal subjects and 177 patients with malignant disease but without metastases. Tests were run 2 hr after tracer injection. Similar ratios were obtained with Tc-99m methylene diphosphonate (MDP) in 220 normal subjects and 451 patients. With MDP, the influence of incubation time (5-10 min in 416 cases, 45 min in 185 cases) on these ratios was determined. DPD was superior to MDP for both ratios. With MDP, prolonged incubation time yielded significantly enhanced ratios; however, the ratios for the DPD were still higher. With either agent and preparation, sacrum-to-ST ratios decreased with increasing subject age, and in patients with malignant disease the ratios tended to be higher than those obtained from normals.