  We find a strong correlation between the extension of the Na-O
anticorrelation observed in red giant branch (RGB) stars and the high
temperature extension of the horizontal branch (HB) blue tails of Galactic
globular clusters (GCs). The longer is the O-depleted tail of the Na-O
anticorrelation observed in the RGB stars, the higher is the maximum
temperature reached by the bluest HB stars in the GC. This result provides a
clear, empirical evidence of a link between the extension of the HB and the
presence of star-to-star abundance variations of proton-capture elements in GC
stars. We discuss the possible interpretation of this correlation.
