Increasing efforts have been made for the development of antibody-directed, tumor-selective cytotoxic agents by coupling cytotoxic agents to antibodies to tumor-associated antigens on the tumor cell surface. Toxins and their subunits, anti-cancer drugs, and radioisotopes are used as the toxic agents for the antibody conjugates. This article discusses the current status of research on antibody conjugates with the enzymatic subunit A-chain of the plant toxin ricin and with the anti-cancer drug methotrexate focusing on the development of the methods of preparation of the conjugates having better biological profile.