  The parsec-scale total intensity structures of BL Lac objects share many
characteristics with quasars: e.g. well-collimated jets and superluminal
motion. However, the jets of BL Lac objects appear to fade much more quickly
than those in quasars and on VLA scales many BL Lacs have structures comparable
to those of low luminosity (FR I) radio galaxies, in which kpc-scale flow
speeds are non-relativistic.
  The region between parsec and kiloparsec scales is therefore one of
transition in BL Lac objects. We have carried out VLBI observations of a small
sample of BL Lac objects at frequencies between 2.3 GHz and 327 MHz in order to
investigate this transition region. Preliminary results for two of these
sources are presented here.
  Coherent structures are detected in these sources out to a distance of
several tens of parsecs. We find evidence for significant changes in jet
structure on scales of a few tens of milliarcseconds, both in terms of the
orientation and collimation of the jets.
