Doxorubicin was modified with five different heterobifunctional reagents to produce drug analogs containing 3'-N-amide or C-13 hydrazone linkage with maleimide. Synthesis and characterization of two new reagents, 4-maleimidobenzohydrazide trifluoroacetate salt (13) and N-(4-maleimidobenzoyl)-6-aminocaprohydrazide trifluoroacetate salt (14) are described here. All Dox maleimido derivatives were conjugated to thiolated anti-carcinoembryonic antigen monoclonal antibody, 11-285-14, via a Michael addition reaction. Antibody-directed cytotoxicity was demonstrated with the MTT assay using combinations of antigen-positive and antigen-negative cell lines. The immunoconjugates prepared from Dox 3'-N-amide analogs are not active in vitro, however, Dox(hydrazone-linked) immunoconjugates are selectively toxic to the CEA positive cell line.