Zoledronic acid (zoledronate) is a new generation bisphosphonate that inhibits osteoclast bone resorption. It was much more potent than other bisphosphonates at inhibiting 1,25-dihydroxyvitamin D3-induced hypercalcaemia in a rat model and calcium release in vitro. A single 5-minute intravenous infusion of zoledronic acid (4 or 8 mg) was significantly more effective than a 2-hour infusion of pamidronic acid (pamidronic acid disodium, pamidronate disodium) [90 mg] in normalising serum calcium levels in patients with hypercalcaemia of malignancy and resulted in a significantly longer median time to relapse (pooled analysis from 2 randomised, double-blind, parallel-group trials). There were no differences in tolerability between zoledronic acid and pamidronic acid in comparative trials; the most common events in pivotal trials were fever, anaemia, nausea, constipation and dyspnoea. Fever, hypophosphataemia and hypocalcaemia were the most common events in a small phase I trial.