This study examines the economic implications of restricting the importation of casein and lactalbumin--dairy proteins used in various food, feed, and industrial products. Under existing legislation and trade agreements, the most extreme restrictions that may be imposed are a 50-percent quota or a 50-percent ad valorem tariff. If either of these were imposed, users of casein would shift to soy-based protein and other ingredients wherever possible, although product quality could suffer. Some casein use would be replaced by skim milk solids, but not enough to significantly affect CCC purchases under the dairy price support program. Import restrictions would increase the cost of producing goods containing casein, and thus raise prices to consumers.