Z decay confronts nonstandard scenarios

We show that recent data from the CERN e+e- collider LEP on the Z line shape and decays give stringent new constraints on mixing of e and τ with exotics and Z-Z' mixing. Even in nonstandard models, where both the visible and the invisible part of the Z width are modified, a fourth light neutrino is unlikely unless substantial mixings between neutrinos and exotics are allowed. If the gluino is detectable at the Fermilab Tevatron then the lighter-chargino mass is tightly constrained (>42 GeV)