Radio phone-ins, or 'talk radio' shows, represent a popular environment in which members of the public at large may discuss the news of the day from their own perspective. This article explores some discursive devices that are used in legitimating, or authenticating, lay speakers' opinions about news in this environment. A number of examples of calls to a talk radio show are examined in order to show the oriented-to importance of 'witnessing' (broadly, claims to first-hand knowledge) in establishing the legitimacy of an opinion. A range of factors are discussed, including: the variety of types of first-hand knowledge that may be invoked; the sequential and interactional contexts in which first-hand knowledge is invoked; and the way in which first-hand knowledge itself may be used not just to legitimate, but to undermine, the status of a caller's contribution to the show's debate.