  Secondary radiation of hadrons from a tau pair produced in electron positron
collisions may constitute an important obstacle for precision measurements of
the production cross section and of branching ratios. The rate for real and
virtual radiation is calculated and various distributions are presented. For Z
decays a comprehensive analysis is performed which incorporates real and
virtual radiation of leptons. The corresponding results are also given for
primary electron and muon pairs. Compact analytical formulae are presented for
entirely leptonic configurations. Measurements of $Z$ partial decay rates which
eliminate all hadron and lepton radiation are about 0.3\% to 0.4\% lower than
totally inclusive measurements, a consequence of the ${\cal O}(\alpha^2)$
negative virtual corrections which are enhanced by the third power of a large
logarithm.
