Decisions about expanding an existing product portfolio and capturing new markets are of critical importance to a firm's financial performance and growth. Yet, important questions remain in regard to the extent to which product and brand extensions contribute to a firm's profit in B2B and B2C markets, respectively, and how firms with corporate brands in these markets should pursue an extension strategy that provides maximum impact on firm profit. The authors theorize and empirically address these questions based on a study of firms listed in the U.S. Fortune 500 published ranking. Findings of this research have important prescriptive implications for the management of B2B and B2C firms' growth-based extension strategy and contribute to B2B theory.