  Correlation functions of matrix-valued fields are not generally known for
massive renormalized field theories. We find the large-N limit of form factors
of the (1+1)-dimensional sigma model with SU(N) X SU(N) symmetry. These form
factors give a correction to the free-field approximation for the N=infinity
Wightman function. The method is a combination of the 1/N-expansion of the
S-matrix and Smirnov's form-factor axioms. We expand the renormalized field in
terms of a free massive Bosonic field as N goes to infinity.
