Nine uremic patients on maintenance hemodialysis who showed wide arterial and/or stable periarticular calcifications in spite of a well controlled hyperphosphatemia were treated with the diphosphonate disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) in doses of 7.5 to 10 mg/kg of body wt/per day for 5 to 9 months. No clinical or biochemical side-effects were noted. A significant reduction of the extent of periarticular calcifications was observed in five patients: two of them had a complete regression of soft-tissue calcifications, and one patient showed a reduction of arterial calcification. EHDP (7.5 to 10 mg/kg of body wt/per day) induced a significant increase of the osteoid volume and osteoid surface without significant modification of the calcification front. No evident effect on bone resorption and on the mineral content of the radius has been observed.