  We measure the absolute branching fraction for D0 --> K- pi+ using partial
reconstruction of B0bar --> D^{*+} X \ell^{-} \bar{\nu}_{\ell} decays, in which
only the charged lepton and the pion from the decay D^{*+} --> D0 pi^+ are
used. Based on a data sample of 230 million B Bbar pairs collected at the
Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B
Factory at SLAC, we obtain the absolute branching fractions of D0 --> K- pi+ =
(4.007 \pm 0.037 \pm 0.072)%, where the first uncertainty is statistical and
the second is systematic.
