  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.
