CD99 is a 32kDa surface glycoprotein that is involved in the migration of leukocytes, cell–cell adhesion and apoptosis of T cells and Ewing’s sarcoma (ES) cells, two cell types with a high level of CD99 expression. Engagement of the molecule induces a rapid death signal that appears to be related to the level of expression of this antigen. The rapid apoptosis induced by agonistic anti-CD99 monoclonal antibodies is of clinical interest in ES, a tumour for which no new drugs have been described as clearly effective in the last 10 years. In this study, we show that an anti-CD99 monoclonal antibody can be used to advantage in association with doxorubicin. Striking effectiveness was observed against local tumours and metastases. No remarkably toxic effects of anti-CD99 monoclonal antibody were found in bone marrow against blood precursors. These results provide the necessary rationale and support for a novel modality of therapeutic intervention, which may have application in the care of patients with ES.