  We derive the mean-field theory of disordered block-copolymers composed of
two monomeric species, combining Edwards' functional method with the replica
technique of disordered systems. In the absence of disorder we recover the
canonical self-consistent field theory of inhomogeneous polymers. In the
presence of sequence disorder the theory can be regarded as a comprehensive,
novel self-consistent treatment of copolymer melts, unifying the weak- and
strong-inhomogeneous regimes. In particular, we study the stability of the
microphase separation transition in a melt of diblock-copolymers, composed of
$N$ monomers and equal $A$- $B$-volume fraction, against the disruptive effect
of disorder. We obtain a phase diagram in terms of the relevant parameters,
namely the rescaled Flory-Huggins parameter $\chi N$ and disorder strength $p$.
