We review the connection between m(t) and the Zb (b) over bar vertex i
n ETC models and demonstrate the power of the resulting experimental c
onstraint on models with weak-singlet ETC bosons. Some efforts to brin
g ETC models into agreement with experimental data on the Zb (b) over
bar vertex are mentioned, and the most promising one (non-commuting ET
C) is discussed in detail.