We study resummed perturbative contributions due to a heavy top-quark. These
renormalon contributions are evaluated for fermion propagators. Results for the
top-quark width are given. Estimates of non-perturbative uncertainties are made
on the \rho-parameter using different schemes of dealing with the Landau-pole.
For the physical top-quark mass the effects are negligible.Comment: 30 pages, 14 figures, 1 table; v2: Ref.19 added, typos corrected,
  final version published in PR

Bettinelli, D.