  Studying the internal structure of exoplanets-host stars compared to that of
similar stars without detected planets is particularly important for the
understanding of planetary formation. The observed overmetallicity of stars
around which planets have been detected may be a hint in that respect. In this
framework, asteroseismic studies represent an excellent tool to determine the
structural differences between stars with and without detected planets. After a
general discussion on this subject, I present the special cases of three
different stars: $\mu$ Arae which has been observed with the HARPS spectrograph
in June 2004, $\iota$ Horologii, that we have studied in detail and will be
observed with HARPS in November 2006, and finally HD 52265, one of the main
targets of the COROT mission, an exoplanets-host star which will be observed
with the COROT satellite during five consecutive months.
