  We study the scheme dependence of the two-loop expression for the
$\rho$-parameter of the Standard Model in the heavy $t$-quark mass limit $m_{t}
\gg m_{w}$. In the $\ms$-scheme the two-loop electroweak correction to the
${\cal O}(m_{t}^{2})$ term in $\dr$ is found greater than the QCD
$\as$-correction.
