To increase the effect of cisplatin on locoregional osteosarcoma, the shortterm effect of hyperthermic isolated regional perfusion (HIRP) with cisplatin (30 mg/L extremity volume) was studied in 28 dogs with spontaneous osteogenic sarcoma, using clinical, radiological, and histological parameters. Thirty days postoperatively, mortality was 14.3%. Total platinum levels at the start of perfusion were 28.2 ? 14.3 mg/L. A significant improvement ( P < 0.001) in clinical score was observed in the overall group at 6 and 12 weeks after perfusion. The radiological parameter showed a stationary X-ray 2 weeks after perfusion and an improved X-ray 6 weeks after perfusion. Overall histological scores showed a moderate effect according to the Huvos classification. No additional therapeutic effect, according to the three parameters, could be demonstrated by increasing the perfusate temperature by 1 "C. HIRP with cisplatin is feasible in the local treatment of spontaneous osteosarcoma in dogs with acceptable locoregional toxicity. However, the histological results were modest, with none of the dogs showing a complete response 6 weeks after perfusion. Therefore, the search for the ideal perfusion agent with substantial contribution to the limb-sparing treatment in human osteosarcoma continues.