  The contribution of the proton polarizability to the ground state hyperfine
splitting in the hydrogen atom is evaluated on the basis of isobar model and
evolution equations for the parton distributions. The contributions of the Born
terms, vector meson exchanges and nucleon resonances are taken into account in
the construction of the proton polarized structure functions $g_{1,2}(W,Q^2)$.
Numerical values of this effect are equal $(2.2\pm 0.8)\times 10^{-6}$ times
the Fermi splitting in electronic hydrogen and $(4.70\pm 1.04)\times 10^{-4}$
times the Fermi splitting in muonic hydrogen.
