The invention relates to the modification of antibodies reactive to human tumor necrosis factor alpha (TNF alpha) to result in anti-TNF alpha antibodies that are substantially non-immunogenic or less immunogenic than any non-modified parental antibody when used in vivo. The invention relates also to peptide molecules comprising T-cell epitopes of the V-regions of the parental antibody which are modified by amino acid alteration in order to reduce or eliminate said T-cell epitopes.