  The two-loop ``top-down'' renormalization group flow for the top, bottom and
tau Yukawa couplings is explored in the framework of supersymmetric grand
unification; reproduction of the physical bottom and tau masses is required.
Instead of following the recent trend of implementing exact Yukawa coupling
unification i) a search for infrared (IR) fixed lines and fixed points in the
m(top)-tan(beta) plane is performed and ii) the extent to which these imply
approximate Yukawa unification is determined. Two IR fixed lines, intersecting
in an IR fixed point, are located. The more attractive fixed line has a branch
of almost constant top mass, 168-180 GeV, close to the experimental value, for
the large interval 2.5<tan(beta)<55; it realizes tau-bottom Yukawa unification
at MGUT approximately. The fixed point at m(top)= 170 GeV, tan(beta)=55
implements approximate top-bottom Yukawa unification at all scales. The fixed
point and lines are distinct from the much quoted effective IR fixed point
m(top)=O(200)GeV sin(beta).
