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I present multiband optical and UV Hubble Space Telescope photometry of thetwo Galactic globular clusters NGC6388 and NGC6441, in order to investigate thenature of the physical mechanism(s) responsible for the existence of anextended blue tail and of a slope in the horizontal branch. Further evidencethat the horizontal branch tilt cannot be interpreted as an effect ofdifferential reddening is provided, while I show that a possible solution ofthe puzzle is to assume that a small fraction of the stellar population in thetwo clusters is strongly helium enriched.

The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC6388 and NGC6441