Paw swelling, or footpad edema, is a convenient method for assessing inflammatory responses to antigenic challenges and irritants. The protocol described in this unit uses carrageenan as the irritant to induce paw edema. Typically, test compounds are assessed for acute anti-inflammatory activity by examining their ability to reduce or prevent the development of carrageenan-induced paw swelling. This model has long been used to assess the anti-inflammatory properties of agents such as nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit prostaglandin production.