A 10-year-old boy with leukaemia-associated hypercalcaemia was treated with aminohydroxypropylidene biphosphonate (AHPrBP previously APD) in a total dosage of 60 mg over 5 days, when the condition failed to respond to rehydration and frusemide and no sustained effect was produced by haemodialysis with a calcium (Ca)-free dialysate. Bone films showed no lytic lesions, and AHPrBP, which is a potent inhibitor of osteoclast-mediated bone resorption was well tolerated and induced a rapid and sustained fall in plasma Ca (from 3.42 to 2.07 mM in 5 days). Plasma magnesium and alkaline phosphatase remained normal. The results could have been affected by other drugs [vincristine, cyclophosphamide, zorubicin (Rubidazone) L-asparaginase and prednisone] which were simultaneously administered. However, the observation that: (1) the response curve of plasma Ca was similar to that reported when AHPrBP was used alone, (2) there was complete inhibition of urinary Ca excretion and (3) hypocalcaemia occurred suggests that AHPrBP was the major cause of the reduction in plasma Ca. AHPrBP should be considered a potential therapy for hypercalcaemia in childhood malignancy.