  The behaviour of the Delta nu =2 CO bands around 2.3 micron was examined by
comparing observed and synthetic spectra in stars in globular clusters of
different metallicity.
  Changes in the 12C/13C isotopic ratio and the carbon abundances were
investigated in stars from 3500--4900 K in the galactic globular clusters M71,
M5, M3 and M13, covering the metallicity range from --0.7 to --1.6. We found
relatively low carbon abundances that are not affected by the value of oxygen
abundance. For most giants the 12C/13C ratios determined are consistent with
the equilibrium value for the CN cycle. This suggests complete mixing on the
ascent of the red giant branch, in contrast to the substantially higher values
predicted across this range of parameters by the current generation of models.
We found some evidence for a larger dispersion of \CDC in giants of M71 of
metallicity [mu] = [M/H] = -0.7 in comparison with the giants of M3, M5 and
M13, which are more metal deficient.
  Finally, we show evidence for lower 12C/13C in giants of globular clusters
with lower metallicities, as predicted by theory.
