In this issue, Glantz and Ong offer a powerful analysis of the tobacco industry's attempt to discredit the scientific evidence on passive smoking, particularly the industry's use of the label "junk science." Environmental epidemiologic studies in other arenas have also been targets for the "junk science" label. Lessons for researchers involved in high-stakes issues in the public policy arena include a need for awareness of competing interests, for transparency concerning funding, and for adherence to rigorous quality assurance and peer review practices. The goal of "sound science" seems an admirable one; it should not, however, be used to dismiss available but uncertain evidence in order to delay action.