  The calculation of hadronic polarizability contribution of the nucleus to
hyperfine structure of muonic hydrogen and helium is carried out within the
unitary isobar model and experimental data on the polarized structure functions
of deep inelastic lepton-proton and lepton-deuteron scattering. The calculation
of virtual absorption cross sections of transversely and longitudinally
polarized photons by nucleons in the resonance region is performed in the
framework of the program MAID.
