  We calculate the two-step contribution to (p,p') and (p,n) reactions at
intermediate energy. We describe the motion of the incident nucleon with plane
wave and compare the contribution from the two-step processes with that from
the one-step processes. To describe the two-step processes, we extende the
response functions into the nondiagonal ones with respect to the momentum
transfer q.
  We performed a numerical calculation for the cross sections of the $^{12}$C,
$^{40}$Ca(p,p') scatterings and the spin longitudinal and the spin transverse
cross sections of the $^{12}$C,$^{40}$Ca(p,n) reactions at 346 MeV and 494 MeV.
We found that the two-step contribution is appreciable in comparison with the
one-step processes in higher energy transfer region for the spin longitudinal
and the spin transverse (p,n) reactions. We also found that the two-step
processes give larger contribution to the spin transverse (p,n) reaction than
to the spin longitudinal reaction. This finding is very encouraging to
interpret the discrepancy between the DWIA calculation and the experimental
results of the spin longitudinal and the spin transverse cross sections.
