The Agency for Healthcare Research and Quality, through its Effective Health Care program, will sponsor an invitational symposium on clinical and comparative effectiveness research methods in June 2009 (dates to be confirmed). The symposium is a follow up to the 2006 AHRQ conference on Emerging Methods in Comparative Effectiveness and Safety; papers presented at that conference appeared in a 2007 Medical Care supplement. The 2009 conference will focus on empirical studies and methodological advances appropriate for publication as a supplement in a peer-reviewed journal. AHRQ is inviting participation in this second symposium through submission of a brief abstract on relevant research by February 13, 2009. Preference will be given to research that can be presented at the symposium as a prelude to publication in the journal supplement and that will be complete or nearly so by early summer 2009.