We present a simple theory and a supporting experimental study of the extent to which block copolymer micelles in a homopolymer matrix can be swollen by relatively low molecular weight homopolymer which is compatible with the copolymer block that forms the micelle cores. The theory is an extension of simple models of copolmer micelles1-3 and predicts the solubilization limit of the added homopolymer, its effects on the micelle size and number density, and the dependences of these quantities on the molecular weights and relative volume fractions of the constituents. The experiments were carried out on systems of PS-b-PEO block copolymers in PS hosts to which homopolymer PEO was added. The experimental results can be understood within the context of the theoretical picture.