 Internet-based health applications can have powerful positive health effects e.g. IOM, 2002: Eng et al., 2000; Gustafson et al., 2000. Research has focused on Internet users as consumers of information, not how they interact with one another, providing advice, consolation, encouragement and pointers to resources. There has been little evaluation of health-related mailing lists, email-based applications that connect millions of people, many with chronic diseases, with one another. The Association of Cancer Online Resources ACOR has teamed with The University of North Carolina UNC to assess the impact of participation on patients, survivors and others including caregivers in 15 cancer-related mailing lists managed by ACOR We are conducting a multi-method evaluation with several elements. In the qualitative component, we are conducting a content analysis of a subset of threaded discussions from archived mailing list pages to identify a comprehensive set of themes and key outcomes. This information will provide a richer understanding of mailing list processes and also will provide checks and balances on the quantitative survey. We also are evaluating the impact of being a subscriber to ACOR mailing lists on a range of outcomes by following a cohort of new subscribers for 4 months from sign-up minimum n1680. Baseline, one and four month web-based surveys with telephone as an option for those who cannot do web surveys will be administered to consenting subscribers. We also are surveying ongoing subscribers who are patients and caregivers minimum n1680. We will disseminate findings to several key audiences, including listowners and members as well as to a broader audience. 