Electronic Journal of Differential Equations, Vol. 2000(2000), No. 15, pp. 1-11. Title: A diffusion equation for composite materials Author: Mohamed El Hajji (Universite de Rouen, France) Abstract: In this article, we study the asymptotic behavior of solutions to the diffusion equation with non-homogeneous Neumann boundary conditions. This equation models a composite material that occupies a perforated domain, in ${\mathbb R}^N$, with small holes whose sizes are measured by a number $r_\varepsilon$. We examine the case when $r_\varepsilon < \varepsilon^{N/(N-2)}$ with zero-average data around the holes, and the case when $\lim_{\varepsilon\to 0}{r_\varepsilon/\varepsilon}=0$ with nonzero-average data. Submitted October 14, 1999. Published February 22, 2000. Math Subject Classifications: 31C40, 31C45, 60J50, 31C35, 31B35. Key Words: Diffusion equation; composite material; asymptotic behavior; $H^0$-convergence.