Eighty-six patients with heavily pretreated progressive bone metastases (52 with breast carcinoma, 17 with prostate carcinoma, and 17 others) were included in 2 studies designed to assess the clinical and biochemical effects of a single 120 mg, 2-hour infusion of pamidronate. No other systemic anticancer treatment or radiotherapy were administered. Pamidronate had a significant beneficial effect, with a reduction in a symptom score measuring pain, World Health Organization performance status, and analgesic consumption and improvement in quality of life when compared with a placebo infusion. Symptomatic improvement corresponded with changes in the rate of bone resorption as indicated by the concentrations of pyridinoline crosslinks in the urine. In patients with the highest rates of bone resorption (N-terminal peptide-bound portion of the collagen crosslink or crosslaps excretion > or = twice that of normal) clinical response or normalization of the rate of bone resorption were rarely observed, with all clinical responses occuring in those patients with bone resorption rates of < twice that of normal. Intriguingly, symptomatic response also correlated with a modest (> 10%) fall in tumor marker levels, suggesting a possible effect of bisphosphonates on tumor activity.