In view of previous animal studies showing that pamidronate (Aredia) can cause renal damage, and human data indicating that pamidronate in doses of 60-90 mg is more effective in the control of tumor-induced hypercalcemia than when given at lower doses, we decided to investigate whether pamidronate 90 mg infused over 60 minutes at weekly intervals had any adverse effects on renal function in patients with bone metastases. Twelve patients, 7 female (all with breast cancer) and 5 male (4 with prostate cancer, 1 with bladder cancer) were entered into the trial. Each patient received weekly intravenous infusions of pamidronate 90 mg in 250 ml normal saline over 60 minutes for 4 weeks. 51Cr-EDTA clearances showed no significant changes in renal function. Urinary N-acetyl-B-D-glucosaminidase/creatinine ratios fluctuated considerably, but no consistent changes were found. No patient with a normal level of urinary beta 2-microglobulin had elevated levels at the end of the trial. Serum creatinine levels did not change significantly, though 1 patient had a corrected serum calcium level of < 2 mmol/L on a single occasion on day 8. No evidence of renal toxicity was detected. However, the possibility that neprohtoxicity would ultimately appear cannot be excluded, and these favourable short-term results cannot be extrapolated to patients with impaired renal function.