The effect of a single dose of pamidronate was studied in 15 patients with hypercalcaemia of malignancy. All patients were hydrated with saline 24 h before and 48 h after treatment. The dose of pamidronate was 30-90 mg intravenously, depending on corrected calcium level after hydration. Patients were retrospectively divided into two groups according to response to pamidronate. Corrected calcium fell to normal or below the upper limit of normal within a median of 3 days after treatment in 7 well controlled patients. In 8 poorly controlled patients corrected calcium failed to return to normal and in 7 of these, corrected calcium increased within 8 days of treatment. The best single indicator of a potent renal mechanism for the hypercalcaemia and also a poor response to pamidronate was a low renal phosphate threshold. Negative isotopic bone scans were also more common in poorly controlled patients.