  We present the full three-loop beta-functions for the MSSM generalised to
include additional matter multiplets in 5, 10 representations of SU(5). We
analyse in detail the effect of three-loop running on the sparticle spectrum
for the MSSM Snowmass Benchmark Points. We also consider the effect on these
spectra of additional matter multiplets (the semi-perturbative unification
scenario).
