The present invention provides for a modified antibody of class IgG, in which at least one amino acid from the heavy chain constant region selected from the group consisting of amino acid residues 250, 314, and 428 is substituted with another amino acid which is different from that present in the unmodified antibody, thereby altering the binding affinity for FcRn and/or the serum half-life in comparison to the unmodified antibody.