At low energies, superstring models lead to an effective E6 theory containing exotic charge -(1/3 quarks, denoted h. Here we work out the consequences of the mixing of h with the b quark, on CP violation, and heavy-neutral-meson systems. This mixing is found to remove the lower bound on mt from and significantly reduces the prediction for. While B0-B» 0 mixing remains unaltered, there is a considerable enchancement of D0-D» 0 mixing from supersymmetric contributions. © 1988 The American Physical Society.