The palliative efficacy of strontium-89 chloride has been evaluated in a prospective double-blind crossover study comparing it with stable strontium as placebo in 32 patients with prostate cancer metastatic to bone. Response was assessed 5 weeks after each treatment. 26 patients were evaluable. Complete pain relief was only reported following strontium-89 injection. Statistical comparison between placebo and strontium-89 showed clear evidence of a therapeutic response to strontium-89 compared with only a limited placebo effect (P less than 0.01).