  We study the sensitivity of the sound speed to relativistic corrections of
the equation of state (EOS) in the standard solar model by means of a
helioseismic forward analysis. We use the latest GOLF/SOHO data for $\ell =
0,1,2,3$ modes to confirm that the inclusion of the relativistic corrections to
the adiabatic exponent $\Gamma_1$ computed from both OPAL and MHD EOS leads to
a more reliable theoretical modelling of the innermost layers of the Sun.
