After a 48-hour rehydration period 28 of 31 patients with cancer-associated hypercalcemia (serum calcium greater than or equal to 2.8 mmol/l) were treated intravenously with the bisphosphonate pamidronate. In three patients fluid repletion with 0.9% saline solution had already normalized serum calcium levels. Pamidronate was given in a single infusion on day 0, the dose of pamidronate adapted to the severity of hypercalcemia. If the serum calcium concentration was greater than or equal to 2.8 mmol/l on day 3, application of pamidronate was repeated. In all patients normocalcemia was restored; mean serum calcium decreased from 3.2 +/- 0.35 on day 0 to 2.15 +/- 0.32 on day 12. Hypercalcemia recurred in 11 patients, seven of these underwent pamidronate treatment according to the same therapeutical regimen. Normal calcium levels were attained in five cases. Side effects were of minor gravity: brief hyperthermia occurred in four patients and transient, asymptomatic hypocalcemia was noticed in nine cases.