I derive and test predictions from the classic Mussa and Rosen (1978) second-degree price discrimination model using data from the United States clothes washer market. I find evidence consistent with price discrimination in the market response to energy efficiency policy changes. Concurrent with the effective dates of both the new 2004 and 2007 federal minimum efficiency and ENERGY STAR standards, within-model clothes washer prices dropped on average. The heterogeneous pattern of price reduction across market segments, and adjustments in the menu of products, were consistent with predictions from the price-discrimination model, and not with a perfectly competitive market.