  We recall the current status of the long-standing 3He problem, and its
possible connection with chemical anomalies on the red giant branch. In this
context, we collect in the literature all the available observations of the
carbon isotopic ratio in field and cluster giant stars. Using the HIPPARCOS
parallaxes, we get constraints on the evolutionary status of the field stars of
the sample. This allows us to identify the stars that have passed the
luminosity function bump and present 12C/13C ratios in disagreement with the
standard predictions of stellar evolutionary models. We determine statistically
what fraction of low mass stars experience an extra-mixing process on the red
giant branch, and are then expected to destroy their 3He at this evolutionary
phase. The high number we get satisfies the galactic requirements for the
evolution of the 3He abundance.
