Abstract: The invention provides a method for identifying positions of an antibody that can be modified without significantly reducing the binding activity of the antibody. In many embodiments, the method involves identifying a substitutable position in a parent antibody by comparing its amino acid sequence to the amino acid sequences of a number of related antibodies that each bind to the same antigen as the parent antibody. The amino acid at the substitutable position may be substituted for a different amino acid without significantly affecting the activity of the antibody. The subject methods may be employed to change the amino acid sequence of a CDR without significantly reducing the affinity of the antibody of the antibody, in humanization methods, or in other antibody engineering methods. The invention finds use in a variety of therapeutic, diagnostic and research applications.