  The recent measurements of the Michel parameters in tau decays enable, for
the first time, a thorough analysis of the leptonic sector. In general, in
models beyond the Standard Model, these parameters will be altered through
changes in the W and Z couplings, and/or through interactions mediated by new
gauge bosons. We perform a complete, model independent analysis of the
constraints imposed by the present data on such boson-mediated interactions,
and point out the existence of useful relations among the couplings.
