The arrangement of peptides which form the hinge region in Fab-Fc recombinant immunoglobulins, restored artificially from Fab and Fc fragments was approached by computation. The architecture of this region in the symmetric (Fab')2-Fc derivatives and in the asymmetric (Fab')1-Fc differs to a considerable extent. In (Fab')2-Fc species but not in (Fab')1-Fc the preferable arrangement appeared to be stabilized predominantly by the mutual interaction of symmetric hinge peptides. It was concluded that the resulted by this interaction rotational restrictions may eventually induce the structural transformations in the molecule, influencing the effector activity of Fc.