This paper examines John Locke's labor theory of ownership from an ecological perspective, and explores its role in western US, property rights disputes. The labor theory of ownership describes how an individual, through application-of labor, can justifiably acquire a private property right to the yield of commonly-held natural resources. The presence of ecosystem processes and services beneficial to humans, coupled with equity and no-harm principles, places limits on the extent to which strong labor-based rights can be justified. Property claims to areas that have not undergone physical transformation due to human labor are less-strongly justified. Rather. than continue in its inappropriate role in support of strong private property rights in the western US, the labor theory can play a new role in justifying and limiting ecosystem management regulation of private and government-owned lands and who should pay. If ecosystem management regulations prevent, reduce, or eliminate harms to ecosystem services and processes, the costs of such management can justifiably fall on private landowners and private users of public lands. If such programs augment existing ecosystem services and processes, costs should fall on the government. (C) 2003 Elsevier B.V. All rights reserved.