With the introduction of preoperative (neoadjuvant) chemotherapy in the treatment of osteosarcoma, an early preoperative evaluation of the effectiveness of chemotherapy is essential, so that treatment may be modified in cases which are not responsive, and so that the surgical margin may be planned. The authors evaluate the accuracy of total body bone scan with Tc99m MDP in determining response to chemotherapy in 43 patients affected with osteosarcoma of the limbs, and preoperatively submitted to two cycles of chemotherapy with MTX i.v. and CDP i.a. All of the cases were submitted to a double bone scan examination, before and after preoperative chemotherapy. A bone scan evaluation using a qualitative method was compared to the percentage of necrosis observed in the tumorous tissue by histological examination carried out after surgery. In 58% of the cases the two values corresponded perfectly, in 28% of the cases bone scan evaluation overestimated response, and in 14% it underestimated it. In order to obtain quantitative preoperative data on response to chemotherapy in osteosarcoma, orientation towards the use of more sophisticated bone scan methods seems to be necessary, with computerized analysis of captation by dynamic measurement after infusion of Tc99m MDP or by radiocompounds with intracellular fixation such as Ga 67.