We study stress relaxation in a strongly segregated lamellar mesophase of diblock copolymers. We consider the extreme limit in which chains are highly stretched and with their junction points confined to narrow interfaces. A lamella can be divided into "stress blobs" at some distance $z$ from the interface, with well defined local modulus $G(z,ω)$ at frequency $ω$. For sliding (compressional) stress the total modulus is transmitted in series (parallel) across the layer. We evaluate the local $G(z,t)$ which shows, for a given height, a very broad spectrum of relaxation times.