Unlike a great deal of research on expert/non-expert communication, most of which is based on written materials, this article focuses on face-to-face communication. The analysis is based on a large corpus of transcribed recordings of medical seminars in rehabilitation centers and of interviews with chronically ill patients suffering from heart conditions. The focus is on procedures of illustration, which are often combined with reformulation procedures. Four main types are described: metaphors, exemplification, scenarios, concretization. Whatever the type of illustration used, participants in face-to-face interaction show a marked preference for procedures which relate abstract medical information to everyday life and experience. After a brief outline of the theoretical approach adopted the analysis proceeds in two steps: first, the emphasis is on techniques employed by the "experts," then, on those used by "non-experts," i.e., patients. This is followed by an examination of the question how the roles of expert and nonexpert are constituted in and by interaction. [Copyright 2003 Sage Publications Ltd.] (LLBA 2003, vol. 37, n. 4)