New constraints on the tau neutrino mass and fourth generation mixing

We present new constraints on the mass $m_{\nu_\tau}$ of the tau neutrino and its mixing with a fourth generation neutrino. From an analysis of the partial widths of tau lepton decays we obtain the following bounds at the 90% confidence level: $m_{\nu_\tau} < 32$ MeV and $\sin^2\theta < 0.007$, where $\theta$ describes the Cabibbo-like mixing of the third and fourth generation neutrinos.