The rate for the production of massive fermions radiated off a pair of
massless fermions is calculated analytically. Combined with the
analytic calculation of the corresponding virtual contribution one
obtains the order $\alpha^2$ correction to the cross section which
is induced by the real and virtual radiation of a pair of massive
fermions by massless fermions.
Approximations valid for
large and for small masses are derived and shown to agree with
earlier calculations.