The influence of nonvanishing quark masses on the total cross section
in electron positron collisions and on the Z decay rate is calculated.
The corrections are expanded in m(2)/s and alpha(s). Methods similar
to those applied for the quadratic mass terms allow us to derive the c
orrections of order alpha(s)m(4)/s(2) and alpha(s)(2)m(4)/s(2). Coeffi
cients which depend logarithmically on m(2)/s and which cannot be abso
rbed in a running quark mass arise in order alpha(s)(2). The implicati
ons of these results on electron positron annihilation cross sections
at LEP and at lower energies in particular between the charm and the b
ottom threshold and for energies several GeV above the b (b) over bar
threshold are discussed.