High energy isospin breaking in technicolor theories

Within technicolor theories, we explore the impact of four-fermion interactions on the fermion mass splittings via explicit breaking of the custodial SU(2)R symmetry. Assuming they do not lead to unacceptably large flavor-changing neutral currents, the question is whether the large b-t quark mass splitting can be accommodated given the experimental limits on ρ-1, where ρ=MW2/MZ2 cos2θW. We argue that this is possible, although further increases in the experimental lower bound on mt may be difficult to accommodate in the present framework. (orig.)