A chimeric mouse-human antibody has been created that recognizes an antigen found on breast cancer cells and melanoma cells. Immunoglobulin constant domains of mouse monoclonal antibody CDI 315B Cγ1 and Cκ, were substituted by the human Cγ1 and Cκ. The CDI 315B variable heavy and light chain regions were PCR amplified from hybridoma RNA and sequenced. Mouse variable V and V regions were joint to human IgG and κ constant regions and subcloned into pcDNA3 expression vectors. The Sp2/0 murine myeloma cells were transfected with expression vectors pcDNA3L and pcDNA3H and the reactivity of chimeric antibodies was tested by indirect ELISA using B16F1 murine melanoma cells as well as MCF7 human breast cancer cells, as antigen.