ABSTRACT This paper looks at, within the context of lean production, how and in what ways employees participate in environmental improvements. The paper uses data from an automobile plant well known for its participative work structures, New United Motor Manufacturing (NUMMI), to look more closely at the dynamics of worker participation in environmental management (i.e. management of pollution and waste). Findings show that while workers possess important contextual knowledge, the importance of process, intra-organizational and external knowledge make the role of specialist staff (both internal and external to the environmental function) critically important for environmental improvements. Additionally, environmental improvements often required a combination of more than one knowledge type. The paper discusses how the culture and management structure at NUMMI and other lean plants encourage this combination. Implications for environmental management, lean production, and future research on worker participation are discussed.