A murine IgG2a monoclonal antibody, termed 6-19, was characterized in terms of its ability to bind to human cell lines and tissues. The hybridoma was selected for antibody binding to multiple human neuroblastoma cultured cell lines but not to peripheral blood mononuclear cells. 6-19 binds to the cell surface of all cultured human nonhematopoietic tumor cell lines tested, to cultured human fibroblasts and endothelial cells, and to nonhematopoietic tumors of many types. It does not bind detectably to any hematopoietic cells, leukemia cells, or lymphomas. In the presence of complement, 6-19 is very cytotoxic to cultured human neuroblastoma cells but not to bone marrow granulocyte-macrophage colony-forming cells. The 6-19 monoclonal antibody may prove useful in the identification or destruction of tumor and stromal cells in bone marrow.