Abstract. We construct a spectral sequence that computes the generalized homology E * ( X α ) of a product of spectra. The E 2 -term of this spectral sequence consists of the right derived functors of product in the category of E * E-comodules, and the spectral sequence always converges when E is the Johnson-Wilson theory E(n) and the X α are L n -local. We are able to prove some results about the E 2 -term of this spectral sequence; in particular, we show that the E(n)-homology of a product of E(n)-module spectra X α is just the comodule product of the E(n) * X α . This spectral sequence is relevant to the chromatic splitting conjecture.2000 Mathematics Subject Classification. 55T25, 55N22, 55P60, 18G10, 16W30.Introduction. The basic tools of computation in algebraic topology are homology theories. Homology theories preserve coproducts, but can behave very badly on products. There are examples of homology theories E and sets of spectra (generalized spaces) {X α }, for which E * X α = 0 for all i and yet E * ( α X α ) = 0. Indeed, we can take E = H,ޑ rational homology, where we have (H)ޑ * (H/ޚp k ) = 0 for all k, but