We propose a simple method, requiring only minimal data, for bounding demand elasticities in growing, homogeneous-product markets. Since growing demand curves cannot cross, shifts in market equilibrium over time can be used to “funnel” the demand curve into a narrow region, bounding its slope. Our featured application assesses the antitrust remedy in the 1952 DuPont decision, ordering incumbents to license patents for commercial plastics. We bound the demand elasticity significantly below 1 in many post-remedy years, inconsistent with monopoly, supporting the remedy’s effectiveness. A second application investigates whether the 1911 dissolution of American Tobacco fostered competition in the cigarette market. (JEL K21, L24, L65, L66, N41, N42, O34)