Assuming precise knowledge of vector boson masses the top quark mass is predicted through its effect in radiative corrections, both in the minimal standard model and in some extensions of it. Deviations from minimality are parametrized in terms of an admixture of I= 1 2 and I=1 Higgs particles in the limit of small vacuum expectation value for the triplet field. Effects due to the interplay between m t and the structure of the Higgs system are discussed.