  In four globular clusters (GCs) a non negligible fraction of stars can be
interpreted only as a very helium rich population. The evidence comes from the
presence of a "blue" main sequence in $\omega$ Cen and NGC 2808, and from the
the very peculiar horizontal branch morphology in NGC 6441 and NGC 6388.
Although a general consensus is emerging on the fact that self--enrichment is a
common feature among GCs, the helium content required for these stars is
Y$\simgt$0.35, and it is difficult to understand how it can be produced without
any --or, for $\omega$ Cen, without a considerable--associated metal
enhancement. We examine the possible role of super--AGB stars, and show that
they may provide the required high helium. However, the ejecta of the most
massive super--AGBs show a global CNO enrichment by a factor of $\simeq$4, due
to the dredge--out process occurring at the second dredge up stage. If these
clusters show no evidence for this CNO enrichment, we can rule out that at
least the most massive super--AGBs evolve into O--Ne white dwarfs and take part
in the formation of the second generation stars. This latter hypothesis may
help to explain the high number of neutron stars present in GCs. The most
massive super--AGBs would in fact evolve into electron--capture supernovae.
Their envelopes would be easily ejected out of the cluster, but the remnant
neutron stars remain into the clusters, thanks to their small supernova natal
kicks.
