The solar interior has been scrutinized by two different and independent probes during the last twenty years with important revisions of the solar model, including a recent heavy element abundancerevision. Today, we get a quantitatively coherent picture (even incomplete) of the solar (stellar) radiative zones. In this review, we recallthe clues for solar gravitational settling definitively established by the seismic determination of the photospheric helium content. We comment also on the need for mixing in the transition region between radiation and convectionin the case of the Sun and of population II stars. We finally list the open questions and the importance to continue more precise investigations of the solar (stellar) radiative zone in detecting gravity modes with the project DynaMICS.