The value of radionuclide bone scanning in the diagnosis of renal osteodystrophy is still debated. In order to re-examine this issue, 25 uremic patients treated by intermittent hemodialysis underwent 99m-Technetium Methylene Diphosphonate (99mTc-MDP) bone scan. They were subdivided into three groups according to quantitative bone histology. Group 1 (N = 8) had pure dialysis osteomalacia, group 2 (N = 7) mixed lesions, and group 3 (N = 10) pure osteitis fibrosa. The scintigraphic studies were interpreted by means of a five point semi-quantitative scale. Using this quantification, all but one group 1 patients had decreased bone tracer uptake, and all patients of group 3 had an increased uptake (chi square test of Yates, P less than 0.001). Among patients of group 2, bone uptake was decreased in the three patients with clearly reduced mineralization front and moderate osteitis fibrosa, but it was increased in all patients with severe osteitis fibrosa and subnormal mineralization front. A quantitative analysis of regional tracer uptake into bone was performed in two patients: one of group 2 and one of group 3. The results obtained clearly corroborated the semi-quantitative findings. Thus, in hemodialysis patients with symptomatic bone disease, the 99mTc-MDP bone scan provides useful information for the differential diagnosis between dialysis-related osteomalacia and secondary hyperparathyroidism. In patients with mixed lesions, the importance of bone tracer uptake appears to depend on the extent of the mineralization front and on the intensity of osteitis fibrosa.