  We present a measurement of $D^0$-$\D0bar$ mixing parameters using the ratios
of lifetimes extracted from samples of $D^0$ mesons decaying to $K^-\pi^+$,
$K^-K^+$, and $\pi^-\pi^+$. Using 91 ${\rm fb}^{-1}$ of data collected by the
BaBar detector at the PEP-II asymmetric-energy $B$ Factory, we obtain a value
$Y = (0.8 \pm 0.4 ({\rm stat.}) {}^{+0.5}_{-0.4} ({\rm syst.}))$%, which, in
the limit of CP conservation, corresponds to the mixing parameter $y =
\Delta\Gamma/2\Gamma$. Using the difference in lifetimes of $D^0$ and $\D0bar$
mesons, we obtain the CP-violation parameter $\Delta Y = (-0.8 \pm 0.6 ({\rm
stat.}) \pm 0.2 ({\rm syst.}))$%.
