Objectives: The c-erbB2 protooncogene is located on human chromosome 17 and encodes a 185-kilodalton transmembrane glycoprotein (ErbB2). Elevated ErbB2 expression or gene amplification has been shown to be associated with a poor prognosis in many cancers. Recently, it has been demonstrated that overexpression of the ErbB2 protein in osteosarcoma is associated with the presence of pulmonary metastasis and decreased survival. To further investigate the role of ErbB2 overexpression in pulmonary metastasis of osteosarcoma, its expression in the primary and metastatic lesions of the same osteosarcoma patients was compared. Methods: We compared the expression levels of ErbB2 receptor protein between the biopsy samples and pulmonary metastatic lesions in each of 19 patients with osteosarcoma who had not presented with metastasis at diagnosis. All archival materials from patients were retrieved and stained with monoclonal antibody CB11 to detect ErbB2 protein. Results: The rate of overexpression was significantly lower in the pulmonary metastatic tumors than in the biopsy samples (11 versus 42%; p = 0.03). Among 8 patients who had shown increased levels of ErbB2 in the biopsy samples, 7 exhibited complete absence of ErbB2 in the pulmonary metastatic lesions. Overall loss of ErbB2 expression was noted in 14 of 19 patients as the initial tumor became metastatic. Conclusions: It is suggested that overexpression of ErbB2 decreases within individual osteosarcomas as they become metastatic. Overexpression of ErbB2 may not play an important role in the development of pulmonary metastases of osteosarcoma. Further data are needed before ErbB2 can be used in making clinical decisions for osteosarcoma patients.