Blogs are extensively used for personal accounts and news reports. In particular, health blogs can be considered as both information sources and communication channels between Science and Society, since they face the growing need for information amongnon-insiders. This study is concerned with the dimension of reality portrayed in blog comment entries; focusing particularly on participants’ representation of facts and their commitment to the truth of the proposition. The framework for this study has been shaped bythe typologies in Chafe (1986), Willett (1988), Van der Auwera and Plungian (1998), Plungian (2001), Marìn (2002, 2004). Data are taken from three health and science weblogs dealing with health issues. Following literature, markers of evidentiality and epistemicmodality were selected in order to assess the writer’s attitude towards the stance (epistemic modality); its reliability and the qualification of source-of-information (evidence of perceptual markers and beliefs, and evidence of inference and reasoning).