 - Measurable primary andor metastatic disease: at least one bi-dimensionally measurable lesion. For patients with neuroblastoma, measurable disease will be defined by the modified International Neuroblastoma Staging System Brodeur et al.1993. For patients with osteosarcoma, measurable lesions are lung metastases and osseous lesions with soft tissue tumor, in exclusion of completely calcified or necrosed lesion at study entry. A patient with an unique osseous lesion without soft tissue mass can be included in the study if the lesion is operable and thus accessible for histological response assessment. 