  The Minimal supersymmetric extension of the Standard Model (MSSM) with light
stops, charginos or pseudoscalar Higgs bosons has been suggested as an
explanation of the too high value of the branching ratio of the Z0 boson into b
quarks (Rb anomaly). A program including all radiative corrections to the MSSM
at the same level as the radiative corrections to the SM has been developed and
used to perform global fits to all electroweak data from LEP, SLC and the
Tevatron. The probability of the global fit improves from 8% in the SM to 18%
in the MSSM. Including the b->s gamma rate, as measured by CLEO, reduces the
probability from 18% to 15%. In the constrained MSSM requiring unification and
electroweak symmetry breaking no improvement of Rb is possible.
