Electronic Journal of Differential Equations, Vol. 2005(2005), No. 77, pp. 1-10. Title: A property of Sobolev spaces on complete Riemannian manifolds Author: Ognjen Milatovic (Univ. of North Florida, Jacksonville, FL, USA) Abstract: Let $(M,g)$ be a complete Riemannian manifold with metric $g$ and the Riemannian volume form $d\nu$. We consider the $\mathbb{R}^{k}$-valued functions $T\in [W^{-1,2}(M)\cap L_{\rm loc}^{1}(M)]^{k}$ and $u\in [W^{1,2}(M)]^{k}$ on $M$, where $[W^{1,2}(M)]^{k}$ is a Sobolev space on $M$ and $[W^{-1,2}(M)]^{k}$ is its dual. We give a sufficient condition for the equality of $\langle T, u\rangle$ and the integral of $(T\cdot u)$ over $M$, where $\langle\cdot,\cdot\rangle$ is the duality between $[W^{-1,2}(M)]^{k}$ and $[W^{1,2}(M)]^{k}$. This is an extension to complete Riemannian manifolds of a result of H. Br\'ezis and F. E. Browder. Submitted June 25, 2005. Published July 8, 2005. Math Subject Classifications: 58J05. Key Words: Complete Riemannian manifold; Sobolev space