  We discuss how models of electroweak symmetry breaking based on strong
dynamics lead to observable contributions to the Z-boson decay width to bbbar
pairs even in the absence of any extended sector responsible for dynamical
generation of the masses of the Standard Model matter fields. These
contributions are due to composite vector mesons mixing with the Standard Model
electroweak gauge fields and lead to stringent constraints on models of this
type. Constraints from unitarity of WW-scattering are also considered.
