On June 4, 1990, the Supreme Court issued its long awaited decisions in McKesson Corp v. Division of Alcoholic Beverages and Tobacco and American Trucking Associations, Inc. v. Smith. Both cases raised the question of whether a taxpayer has a right to a refund of unconstitutional state taxes. This article analyzes these decisions separately and considers the implications of these decisions on future state tax litigation. The article has two purposes: first, to analyze the McKesson and American Trucking Association cases; and second, to consider their implications for future constitutional challenges to state taxes. The article concludes by stating that the two cases are of enormous significance because the Due Process Clause requires that states grant meaningful retroactive relief when they compel taxpayers to pay taxes that are later found to be unconstitutional.