54 patients with malignant hypercalcemia were treated with either dichloromethylene bisphosphonate (Cl2MBP) or aminobutane bisphosphonate (AHButBP). Both compounds infused intravenously (i.v.) were rapidly effective in lowering serum calcium to normal range and a potency ratio between Cl2MBP and AHButBP could be roughly estimated as 1:100-250. 600 mg of Cl2MBP infused in one day over 9 h in nine patients were only slightly less effective (serum calcium from 12.3 +/- 1.7 to 10.1 +/- 1.1 SE, mg/dl) than 3300 mg infused in 11 consecutive days (13.4 +/- 1.9 to 9.3 +/- 1.2 SE, mg/dl). Thus the effectiveness of treatment with Cl2MBP was related better to the overall time of infusion than to the cumulative dose administered. This could not be demonstrated in a similar trial using AHButBP. 1600 mg Cl2MBP daily p.o. was unable to prevent the relapse of hypercalcemia in four patients after a treatment course with i.v. bisphosphonates. 100 mg of Cl2MBP intramuscularly maintained serum calcium within the normal range in two out of eight patients; however, weekly infusions of either Cl2MBP or AHButBP prevented the relapse of hypercalcemia in eight similarly treated patients for several weeks. Providing that adequate dosages are adopted, parenteral Cl2MBP and AHButBP may be a useful measure for controlling hypercalcemia in patients with carcinoma.