Twenty eight (14%) out of 196 patients in a regional dialysis population were found to have serum aluminum levels greater than or equal to 5 mumol/L or 135 micrograms/L; 21 consented to undergo a bone biopsy to identify the spectrum of renal osteodystrophy associated with this degree of hyperaluminemia. Both the Aluminon reagent and the acid solochrome azurine (ASA) stain were used to identify aluminum deposits. A control group of 13 patients with biochemical and histological evidence of severe secondary hyperparathyroidism was used to contrast the measured parameters of bone histology in the hyperaluminemic group. Al(OH)3 was used as the principal phosphate binder in all patients. In the hyperaluminemic group, 67% had either dialysis osteomalacia or aplastic bone lesions, and all except one aplastic lesion were positive for bone surface aluminum deposits by the Aluminon stain. The Aluminon stain was also positive in one of three cases of osteitis fibrosa and three of four mild lesions, whereas it was negative in all biopsies from the control group. However, the ASA stain was positive in all biopsies from the hyperaluminemic group and in 11 of 13 control biopsies from the patients with "pure" osteitis fibrosa. For all biopsy data from both groups, there were significant (P less than 0.01) negative correlations between the ASA-stained surface aluminum deposits and resorption indices (total eroded surface, r = -0.68; surface osteoclast counts, r = -0.53) and indices of bone formation (surface osteoblast counts, r = -0.61; mineral apposition rate, r = -0.63; bone formation rate, r = -0.69). These correlations were not significant for Aluminon-stained surface deposits with the exception of the bone formation indices, which had lower correlation coefficients (r = -0.44). These data suggest that hyperaluminemia greater than or equal to 5 mumol/L has a predictive value to identify impaired mineralization in dialysis patients that is high enough to affect clinical decision making. However, the more sensitive ASA stain identifies surface aluminum across the whole spectrum of renal osteodystrophy and is consistent with a toxic role for aluminum at any level of exposure.