Strontium-89 (89Sr) is currently used for the treatment of painful bone metastases. This study reports the use of low-dose carboplatin as a radiosensitizer in 89Sr radioisotope therapy. The study design comprised two groups: 15 patients treated with 89Sr (148 MBq) followed by carboplatin (100 mg m-2 at 7 and 21 days) and 15 patients treated with 89Sr alone. Their pain response was assessed 8 weeks post-injection. Follow-up was continued for up to 1 year in the survivors. Twenty-seven patients were evaluable. A pain response was observed in 20 of 27 (74%) patients. The pain response in the patients treated with 89Sr and carboplatin was clearly superior to that seen in the patients treated with 89Sr alone (P = 0.025), whereas survival was only marginally better in the combined treatment group (8.1 vs 5.7 months, P = 0.19). No clinically significant adverse effects or myelosuppression by carboplatin were observed. Low-dose carboplatin enhances the effects of 89Sr radioisotope therapy on pain from bone metastases.