We present results for the three-loop top quark contributions to the
rho parameter in the limit of large top quark mass. The simultaneous
dependence on the mass of the Higgs boson M_H and the mass of the top
quark m_t is obtained from expansions in the range of M_H around
m_t and in the limit M_H » m_t. In combination with the previous
result for M_H = 0 the dependence of the rho parameter on the
leading Yukawa contributions, i.e. on m_t and M_H, is well under
control for all mass values of practical importance.
The effects lead to a shift in the W mass in the order of 5 MeV and
are relevant for precision measurements at TESLA.
