Previous efforts addressing binary blends of a block copolymer and a parent homopolymer have principally employed ordered copolymers in either the intermediate- or strong-segregation regimes. In this work, blends composed of a disordered (75/25)-b-(50/50) poly[(styrene-r-isoprene)’-b-(styrene-r-isoprene)"] (S/I)’-b-(SII)" random diblock copolymer (RBC) and homopolystyrene (hS) have been investigated. Blend morphologies, characterized by transmission electron microscopy are correlated with hS concentration and molecular weight, as well as with changes in the hS T-g, as measured by thermal calorimetry. At low hS fractions (up to 20 wt % hS), the S/I block sequences in the RBC induce competition between attractive and repulsive interactions with hS molecules, resulting in the formation of thin hS channel structures in a continuous RBC matrix. An increase in hS concentration or molecular weight serves to broaden the channels until the morphology resembles macrophase-separated hS domains containing micelle-like RBC dispersions. In blends with relatively high hS fractions (greater than 80 wt % hS), repulsive interactions between RBC and hS molecules are responsible for the formation of macroscopic RBC domains in a continuous hS matrix. These blend morphologies demonstrate that localized interactions between homopolymer molecules and each block of a copolymer exist, and can be probed, in the disordered state.