  A Riemannian manifold $M$ is said to satisfy the Omori-Yau maximum principle
if for any $C^2$ bounded function $g:M\to \Bbb R$ there is a sequence $x_n\in
M$, such that $\lim_{n\to \infty}g(x_n)=\sup_M g$, $ \lim_{n\to \infty}|\nabla
g(x_n)|=0$ and $\limsup_{n\to \infty}\Delta g(x_n)\leq 0$. It is shown that if
the Ricci curvature does not approach $-\infty $ too fast the manifold
satisfies the Omori-Yau maximum principle. This improves earlier necessary
conditions. The given condition is quite optimal.

Differential Geometry