  Recent improvements in globular cluster colour-magnitude diagrams, coupled
with an increase in large-sample spectroscopic abundance studies of cluster
giants, finally allow some attempts at a statistically meaningful comparison of
the chemical compositions of red giant branch (RGB) and asymptotic branch (AGB)
cluster stars. We review some of the extant data here, concluding that in a few
clusters the AGB stars show on average smaller amounts of high-temperature
proton-capture synthesis products (low oxygen, high sodium and aluminum) at
their surfaces than do the first-ascent RGB stars. This suggests that those RGB
stars with envelopes that have been enriched with proton-capture material also
have high helium contents. Such stars after the He-flash then take up residence
on the bluest parts of the horizontal branch (as a consequence of their high
envelope helium), probably never to return to the AGB during subsequent
evolutionary stages.
