The analgesic effect of salmon calcitonin was tested by a double-blind clinical randomized controlled trial in 40 female patients with painful osteolytic metastases. Twenty patients were administered (daily) 100 IU of salmon calcitonin subcutaneously over 28 days, while the other 20 were administered identical ampoules containing 2 ml of physiological solution over the same period of time. The basic treatment (chemotherapy, hormone therapy) was not changed during the trial, and had to be stabilized for a minimum of 3 months prior to the trial. The effect of calcitonin was monitored with respect to daily analgesic consumption, duration of pain, patient's functional capacity, patient's own assessment of pain, and assessment of efficacy by the investigator. Statistically significant differences were established in terms of reduced analgesic consumption, shorter duration of pain and the patient's subjective assessment of pain duration and intensity; the difference was not statistically significant with regard to patient's functional capacity. The objective assessment of the analgesic effect of calcitonin by the investigator showed the drug to be extremely useful in 3 patients and moderately useful in 11 patients; 3 instances of 'moderately useful' were observed in the placebo group. No changes were observed in serum calcium levels; there were likewise no skeleton changes as established by X-rays and bone scintiscans before and at the end of treatment. The trial has shown calcitonin to produce a pronounced analgesic effect in breast cancer patients with painful osteolytic metastases.