The effect of two different dialysate solutions with a calcium concentration of 1.25 and 1.75 mmol/l was evaluated in 14 patients, using a cross-over design. Patients were treated with each solution during a period of 6 months. Treatment with calcium supplements, vitamin D and aluminium hydroxide was adapted weekly, according to the results of blood chemistry. PTH, SAP, and ionized calcium were determined monthly, bone density with DXA and QCT before and after 6 months of treatment. During treatment with both 1.25 and 1.75 calcium dialysate (cad), the control of serum calcium and phosphate was similar. PTH did not change during either treatment. SAP decreased during treatment with 1.75, but remained stable with 1.25 mmol/l cad. Bone density evaluated with DXA remained unchanged during both treatments. QCT measured bone density increased from 101.29 +/- 13.50 to 106.79 +/- 13.14 mg/ml in the 1.75 cad group, while it did not vary in the 1.25 cad group, (107.75 +/- 13.48 versus 108.97 +/- 13.40 mg/ml). It is concluded that lowering the calcium content of the dialysate does not negatively influence the control of serum calcium and phosphate, nor does it aggravate hyperparathyroidism when vitamin D is administered simultaneously. Under the present conditions, osteopenia and possibly bone mineralization improve only in the group dialysed with 1.75 Ca.