We evaluated the effectiveness of Re-186-HEDP in 25 patients with painful metastatic bone disease. Twenty-five patients with known prostatic (n = 19), non-small-cell lung cancer (n = 1) and breast cancer (n = 5) and multiple confirmed skeletal metastases were studied. All were taking analgesics daily (nonsteroidal antiinflammatory drugs/opiates). Re-186-HEDP (mean 35.2 mCi) was administered and patients were monitored for at least 50 days. In five patients, a repeat dose was administered 9 to 10 weeks later. The evaluation of the analgesic effect was based on a "pain diary" and by recording the use of analgesics. In 80% (20 of 25) of the patients, the effect was significant palliation, moderate in 3 patients (12%), and insignificant in 2 (8%). No significant myelotoxicity was observed. Transient pain flare was recorded in 8 of 25 patients. These results indicate that Re-186-HEDP can offer pain palliation in patients with painful bone metastases without being complicated by significant myelotoxicity.