  The ongoing searches for Higgs-boson signals in data taken at the CERN LHC
and the Fermilab Tevatron crucially rely on the decay channels H -> Z l l and H
-> W l nu. We present a precision study of the partial widths of these decay
channels including the full one-loop electroweak corrections and the dominant
contributions at two and three loops, of O(G_F^2 m_t^4), O(G_F m_t^2 alpha_s),
and O(G_F m_t^2 alpha_s^2). Since the invariant mass of the off-shell
intermediate boson is relatively low in the mass window 115 GeV < m_H < 129 GeV
of current interest, lepton mass effects are relevant, especially for the tau
lepton.
