Since the majority of patients with osteosarcomas of the limbs develop lung metastases, radiotherapy and/or chemotherapy are used as adjuvant therapy immediately after treatment of the primary. This article questions the roles of radiotherapy and chemotherapy in this instance. A brief review of previous non-randomized studies is made. The overall conclusion seemed to be that although adjuvant chemotherapy resulted in a higher survival of patients with osteosarcoma, in comparison with historical controls, this form of treatment has not proven to be superior to the benefit achieved by lung irradiation. In the light of these studies, the Clinical Cooperative Group Radiotherapy/Chemotherapy (E.O.R.T.C.) and the International Society for Pediatric Oncology (S.I.O.P.) have initiated a prospective, randomized trial comparing chemotherapy, radiotherapy of the lungs and a combination of both treatments. The details of these treatments are given. This trial will try to answer very fundamental questions on adjuvant therapy in osteosarcomas. Active participation of as many medical centres as possible is requested.