Background: The goal of this presentation is to discuss a four-stage model of consumer participation in healthcare policy and decision making. The model is based on several propositions. First, it proposes four roles (stages) of consumer participation that can be defined by two dimensions: credibility and legitimacy. Credibility refers to the degree to which the participant is perceived as representing other consumers and/or the public. Legitimacy is the degree to which the participant is regarded as knowledgeable and accepted by those within the decision-making bodies. Second, we believe there are strengths and weaknesses in each stage. As a result, different skills and experiences are needed by consumers to be effective in each role (stage). Third, while the most effective consumer participants are those in Stage 4 (perceived as credible and legitimate) the most effective healthcare systems are those that encourage and support consumers in all four roles. The presentation discusses the four-stage model using the example of consumer participation in the reform of Canada's blood system following the tainted blood tragedy of the 1980's. Canada, like many countries, experienced widespread infection as a result of tainted blood. It is widely acknowledged that Canada was pushed not only to provide compensation to tens of thousands of those infected but also to conduct a full-scale inquiry and to overhaul the entire blood system as a result of effective consumer participation. This presentation describes the roles and actions of participants in each of the four stages, as well as the factors contributing to success and failure in each stage. In Stage 1, individual activists, unfettered by organizational constraints, brought public attention to the problems. In Stage 2, advocates representing groups of affected individuals, mobilized public support to effectively demand for an inquiry and compensation. This led to Stage 3, where consumers with expertise were invited to participate as members of expert groups and advisory councils to propose reforms, new guidelines, and standards. Finally, in Stage 4, we saw the emergence of independent, consumer groups who serve as watchdogs to hold the system accountable and to facilitate communication between consumers and the system. The presentation concludes with the lessons learned from the experience of the blood system and the potential roles for consumers in other areas of healthcare policy.