  We present a measurement of the absolute branching fraction for $D^0 -> K^-
pi^+$ using the reconstruction of the decay chain $Bbar -> D^{*+} X l^- nubar
$, $D^{*+} -> D^0 pi^+$ where only the lepton and the low-momentum pion from
the $D^{*+}$ are detected. With data collected by the CLEO II detector at the
Cornell Electron Storage Ring, we have determined $Br(D^0 -> K^- pi^+)= [3.81
+- 0.15(stat.) +- 0.16(syst.)]%$.
