Recent results on the entirely analytic
calculation of second order corrections to massive
quark pair production vertices induced by light quark flavours are
reviewed.
Based on the method presented in this talk the second order effects of
the insertion of any massless one-loop
vacuum polarization into the gluon line of
the first order diagrams can be determined. The behaviour of the
corrections at threshold for vector and axial-vector current induced
massive quark production is discussed.