  This paper investigates the effect of microscopic diffusion of helium and
heavy elements on the location of the Red Giant Branch Luminosity Function Bump
in Population II stellar models. To this aim updated evolutionary models taking
into account diffusion from the Main Sequence until the Zero Age Horizontal
Branch have been computed. The observational luminosity difference between the
RGB bump and the ZAHB, as collected for a sample of galactic globular clusters,
has been compared with the corresponding theoretical values obtained by
adopting both canonical and diffusive models. We find that the effect of
diffusion, even if slightly improving the agreement between observations and
theory, is negligible with respect to the observational uncertainties. In any
case the theoretical predictions in models with and without diffusion appear in
agreement with the observational results within the estimated errors. Thus
canonical models can be still safely adopted, at least until much more accurate
observational data will be available.
