  Using the ARGUS detector at the $e^+ e^-$ storage ring DORIS II, we have
measured the Michel parameters $\rho$, $\xi$, and $\xi\delta$ for
$\tau^{\pm}\to l^{\pm} \nu\bar\nu$ decays in $\tau$-pair events produced at
center of mass energies in the region of the $\Upsilon$ resonances. Using
$\tau^\mp \to \rho^\mp \nu$ as spin analyzing tags, we find $\rho_{e}=0.68\pm
0.04 \pm 0.08$, $\xi_{e}= 1.12 \pm 0.20 \pm 0.09$, $\xi\delta_{e}= 0.57 \pm
0.14 \pm 0.07$, $\rho_{\mu}= 0.69 \pm 0.06 \pm 0.08$, $\xi_{\mu}= 1.25 \pm 0.27
\pm 0.14$ and $\xi\delta_{\mu}= 0.72 \pm 0.18 \pm 0.10$. In addition, we report
the combined ARGUS results on $\rho$, $\xi$, and $\xi\delta$ using this work
und previous measurements.
