We investigate the extent to which a grocery retailer merger has different effects on the prices of national and store brands. Using retail scanner data, we retrospectively analyze a food retail acquisition in a large United States city. We focus on fluid milk and ready-to-eat cereal categories, which represent a relatively homogenous and a relatively differentiated product category, respectively. We use a difference-in-difference estimation framework to obtain the causal effect of the acquisition on prices for the acquiring retailer. Our findings provide evidence that store brands in differentiated product categories could allow a retailer to improve its market power.