The aim of this study was to evaluate the value of three-phase dynamic bone scintigraphy (TPBS) in the assessment of the response of bone sarcomas to pre-operative chemotherapy and to correlate serial scintigraphic changes with histological findings. The study group comprised 27 patients (osteogenic sarcoma, n = 20; Ewing's sarcoma, n = 5; malignant fibrous histiocytoma, n = 2) with a mean age of 19.2 years. All patients received 99Tcm-methylene diphosphonate TPBS before and after pre-operative chemotherapy. Each phase of the imaging procedure was interpreted qualitatively and quantitatively. The percentage of tumour necrosis was analysed on resection materials following surgery. Histologically, 12 patients were non-responsive (tumour necrosis less than 90%) and 15 patients were responsive (tumour necrosis more than 90%). A decrease in the tumour blood flow ratio and extension were the most notable findings in the responders. The mean change in the tumour blood flow ratio following therapy was 58.7 +/- 8.3% and 19.9 +/- 26.6% (P < 0.005) in responders and non-responders respectively. The accuracy of three-phase imaging and static bone scintigraphy was 88% and 74% respectively. Since bone scintigraphy is a valuable technique owing to its ability to detect distant metastases in clinically early disease, TPBS should be helpful in monitoring therapy effects without any additional cost or radiation dose.