  For a manifold with nonpositive curvature, the Martin boundary is described
by the behavior of normalized Green's functions at infinity. A classical result
by Anderson and Schoen states that if the manifold has pinched negative
curvature, the geometric boundary is the same as the Martin boundary. In this
paper, we study the Martin boundary for rank 1 manifolds admitting compact
quotients. It is proved that a residual set in the geometric boundary can be
identified naturally with a subset of the Martin boundary. This gives a partial
answer to one of the open problems in geometry collected by Yau. Our proof is a
modification of an argument due to Ancona.
