The invention provides therapeutic or diagnostic antibodies with modified N— or C-terminal sequences that are enriched with lysine or tyrosine residues. These lysine or tyfosine residues can be used to couple radioisotopes, cytotoxic agents, or detectable labels. The increased stoichiometric ratios of these agents in the antibody conjugates lead to improved therapeutic efficacy or enhanced detection sensitivity. Non-limiting examples of antibodies suitable for the present invention include anti-CD22, anti-ErbB2, anti-VEGF, anti-EGFR, anti-VEGFR, anti-Her-3, anti-Her-4, anti-CEA, anti-CTLA-4, anti-CD4, anti-CD3, anti-CD20, anti-TNF-a, anti-CD11a, anti-Lewis Y antigen, anti-TrailR, anti-IL2R, anti-CD30, anti-CD146, anti-CD147, anti-alpha V integrin beta, anti-CD19, anti-GD2, anti-3H11, anti-EBV, anti-HIV, anti-HBV, anti-HCV, and other disease-specific antibodies.