Two hundred and fifty-seven patients were studied with bone-seeking radiopharmaceuticals. They were randomly divided into three groups. Two groups were injected with two different 99mTc-methylene diphosphonates from two manufacturers (MDP 1 and MDP 2) and the third group with 99mTc-dicarboxypropane diphosphonate (DPD). DPD was found to be superior with respect to blood clearance, femur to soft tissue ratio and subjectively assessed image quality. There seemed to be no marked differences between the bone-seeking agents in the visualisation of pathological foci. The image quality seemed to be better in the MDP 2 group than in the MDP 1 group but they were similar in other respects. The femur to soft tissue ratio decreased with increasing age in the DPD group but not in the MDP groups. With all agents worsening of scan quality with increasing age was noted and the image quality was better with men than with women. When short incubation times of radiopharmaceuticals were used before injection, the bone to soft tissue ratio was lower and the scan quality was poorer than with incubation times longer than 20 min.