On the basis of a retrospective assessment of aluminium content in the bones and morphometric findings in spongy bones of patients maintained on long-term dialyses a trial was undertaken of demonstration of a possible causative effect of this metal on the development of osteomalacia. The analysis included also the role of aluminium in the development of intravitally occurring fractures of bones in these patients. A biopsy specimen was taken from the iliac ala with a modified Bartelheimer's needle. The study comprised two groups of patients. The first one included 10 patients in a mean age of 38.2 +/- 6.6 years remaining, on the average, since 72.3 +/- 33.6 month who had previously evidence of fractures demonstrated clinically and radiologically. In the second group 12 patients of a mean age of, 41.9 +/- 6.8 years on dialyses since 40.3 +/- 12.2 months with demonstrated subperiosteal resorption, and patients with normal radiological appearance of the skeleton were studied. The patients were dialysed using a dialysate prepared from water not previously adapted and containing Al in a concentration of 0.135 +/- 0.102 mg/l. The diagnosis of osteomalacia was based on the morphometric method of Bordier (6). In both studied groups a highly significant rise was demonstrated in the concentration of Al in the spongy bone, and pathological fractures were closely related to the morphometric markers of osteomalacia. Aluminium cumulation in the bone tissue of patients with fractures exerted a significant effect on an increase of osteoid volume and reduction of mineralization fronts, and demonstrated a directly proportional relationship with the time of treatment with dialyses and overall exposure to aluminium in the dialysing fluid. In the group with osteomalacia a linear trend was observed in the increase of osteoid volume related to aluminium retention in spongy bone.