The effect on electroweak corrections of anomalous interactions of the top quark with the Z0 is studied. Such anomalous terms are expected to arise in the context of dynamical symmetry breaking. It is shown that, depending on m(t), the whole set of radiative-correction parameters can be relevant. This set consists of three observables coming from the vacuum polarization graphs plus the correction to the Z0bbBAR vertex. The recent data coming from collider experiments are used to place bounds on the anomalous terms. The same observables are evaluated in a simple renormalizable model in which the top quark mixes with an isosinglet up-type quark.