We measured radial velocities of 21 white dwarf-red dwarf binaries to
learn whether their components are dose enough now to have shared a co
mmon envelope sometime in the past. Of the 14 for which we have adequa
te data, five are close binaries, while the other nine appear to be wi
dely separated with no previous common envelope evolution. For the for
mer five, some mass transfer likely occurred, so the current masses of
the corresponding red dwarfs may vary from their initial masses, and
this should be accounted for in derivations of the initial mass functi
on for star formation at the very low-mass end of the main sequence.