Using Collins and Evans' (2002) concept of interactional expertise, this article examines the online activities of three bloggers diagnosed with bipolar disorder. It argues that by combining medical knowledge with their situated experiences, and by utilizing the affordances of blogs, these bloggers have become a new type of stakeholder, the online expert mediator. Collins and Evans' concept is extended by taking into consideration the role of the medium through which interactional expertise is displayed and by showing that its bi-directional character is more substantial than they had envisaged. The rise of this new stakeholder category denotes a possible turn from community activism to exceptional entrepreneurial selves. Despite views that the internet would have broad democratizing effects, the findings show that the high standing of online expert mediators is not the result of a subversive use of this medium, but of a dynamic alliance with 'traditional' experts and of a strong media presence.