  The rate for the final state radiation of hadrons in leptonic $Z$ decays is
evaluated, using as input experimental data for $\sigma (e^+e^-\to hadrons)$ in
the low energy region. Configurations with a lepton pair of large and a
hadronic state of low invariant mass are dominant. A relative rate
$\Gamma_{l\bar l had}/\Gamma_{l\bar l}=6.3\times 10^{-4}$ is calculated. This
result is about twice the prediction based on a parton model calculation with a
quark mass of $300$ MeV. The rate for secondary production of heavy quarks is
calculated in the same formalism.
