Political advertising by interest groups trying to influence public policy has proliferated recently. Formerly the preserve of election campaigns, advertising has spread to policy arenas, such as abortion, trade, and health care. This article examines group lobbying for and against President Clinton’s health care reform plan. Using a study of advertisements, a content analysis of news coverage, interviews with half a dozen leading figures in the debate during the spring of 1995, and an analysis of three national public opinion surveys designed to gauge the public response to health care ads, we investigate the media campaign on health care. Ads directed against the Clinton plan played a crucial role in the public’s attaching negative connotations to some of its key elements. Grassroots campaigns can work either by mobilizing public opinion or by persuading political leaders that grassroots opposition exists to a particular program.