Empirical results from experimental economics and neuroscience have uncovered regularities in human behavior that may provide a base for new approaches to welfare theory and economic policy. These empirical findings do not challenge basic economic concepts but they do imply that our assumptions about "rational behavior", "opportunity cost", and "social welfare" should be revised using sound scientific evidence and methods. This research has the potential to make benefit-cost analysis more reflective of how people value gains and losses, and more responsive to considerations of environmental and social responsibility. (C) 2007 Elsevier B.V. All rights reserved.