  We present our recent results on mm-wave CO observations of proto-planetary
nebulae. These include high-resolution interferometric maps of various CO lines
in three well known bipolar PPNe: M1-92, M2-56 and OH231.8+4.2. The global
properties of the high velocity molecular emission in post-AGB sources have
been also studied, by means of high-sensitivity single dish observations of the
J=1-0 and 2-1 lines of 12CO and 13CO. We discuss the implications of these
results to constrain the origin of the post-AGB molecular high-velocity winds
and the shaping of bipolar PPNe and PNe. In addition, we also present the
results of an interferometric map of the molecular envelope around the luminous
high-latitude star 89 Her, a low mass post-AGB source which is also a close
binary system.
