The mass shift Delta m(N) of a nucleon in the finite temperature pion
gas is calculated in the case of an arbitrary nucleon momentum. A gene
ral formula is used which relates the in-medium mass shift Delta m(E)
of a particle to the real part of the forward scattering amplitude Re
f(E) of this particle on the constituents of the medium and its applic
ability domain is formulated. The mass shift of the nucleon in thermal
equilibrium with the pion gas is also calculated. (C) 1997 Published
by Elsevier Science B.V.