We study the Yamabe invariant of manifolds obtained as connected sums along
submanifolds of codimension greater than 2. In particular: for a compact c
onnected manifold M with no metric of positive scaler curvature, we prove t
hat the Yamabe invariant of any manifold obtained by performing surgery on
spheres of codimension greater than 2 on M is not smaller than the invarian
t of M.