Let
p
(
x
,
y
)
p(x,y)
be the transition function for a symmetric, irreducible, transient Markov chain on the countable set S. Let
η
t
{\eta _t}
be the infinite particle system on S with the simple exclusion interaction and one-particle motion determined by p. A characterization is obtained of all the invariant measures for
η
t
{\eta _t}
in terms of the bounded functions on S which are harmonic with respect to
p
(
x
,
y
)
p(x,y)
. Ergodic theorems are proved concerning the convergence of the system to an invariant measure.