  We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to
examine them for anomalous chemical abundances. In particular, we study the
strength of the 12CO and 13CO absorption bands that have been found diminished
and enhanced, respectively, in similar studies of CVs.
  All our systems show CO abundances that are within the range observed for
single stars. The weakest 12CO bands with respect to the spectral type are
found in the pre-CV BPM 71214, although on a much smaller scale than observed
in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account
that our sample is subject to the present observational bias that favours the
discovery of young pre-CVs with secondary stars of late spectral types, we can
conclude the following: 1) our study provides observational proof that the CO
anomalies discovered in certain CVs are not due to any material acquired during
the common envelope phase, and 2) if the CO anomalies in certain CVs are not
due to accretion of processed material during nova outburst, then the
progenitors of these CVs are of a significantly different type than the
currently known sample of pre-CVs.
