Commentators have bemoaned the role that petitions and citizen suits play in driving the regulatory agendas of environmental agencies. The argument is that these forms of public participation too frequently distract agencies from the priorities that experts believe should be the focus of regulatory efforts. Using data from the listing of species protected under the U.S. Endangered Species Act, we examine whether petitions and citizen suits result in suboptimal agenda-setting by agencies. We find that petitions and litigation result in the identification of species that are at least as deserving of protection under the Act as species identified by the agency on its own. Our results raise the possibility that public participation, by collecting diffuse information about environmental conditions, might help improve the performance of environmental agencies.