A prospective investigation of two different radionuclide imaging techniques for the skeleton--technetium-99m phosphonate and gallium-67 citrate--was carried out prior to biopsy in fifty-five patients with primary bone tumors of the extremities and limb girdles. The study showed that the technetium-99m phosphonate scans were not useful in separating benign from malignant lesions or in defining reliably the local extent of malignant tumors. Gallium scans were more accurate in delineating the local extent of malignant tumors and may provide better indentification of benign tumors.