  The electroweak corrections induced by a heavy top on the main precision
observables are now available up to O(g^4 mt^2/mw^2). The new results
significantly reduce the theoretical uncertainty and have a sizable impact on
the determination of sin^2theta_eff. We give precise predictions for mw and the
effective sine in different renormalization schemes, estimate their accuracy,
and discuss the implications for the indirect determination of M_H. From the
present data for sin^2theta_eff we obtain M_H = 127 +143 -71 GeV (or M_H < 430
GeV at 95% C.L.).
