Through an examination of several events dealing with Aids in the 1980's and 1990's, the author analyses major transformations which have affected the field of national media during this period. The fact that so much media coverage has been given to Aids shows that events concerning activities within a field as autonomous as that of medecine have a tendency today to become events just like any other. In the first part, the author shows that the weight of journalistic (and indeed economic and political) consideration is growing in both the selection and the construction of events in the medical domain. These swing between, on the one hand, the regime of " obligatory events " (scientific announcements) and, on the other, the new regime of the " unexpected events " (scandals or polemics). After demonstrating the slow emergence of media attention to the French " infected blood scandal " cannot be attributed only to the work of a handful of journalists or to the caracteristics of the affair, the author explains in a second part that the specific importance of this affair can be explained by changes in the journalistic field. The " infected blood scandal " enables one to understand the general structure of the field of journalism, which has come to be increasingly dominated by commercial imperatives, as exemplified by the growing role of television in the prioritisation and treatment of events. At a second level, the study of the journalists who covered this affair, analysed, through the changes in recruitment on the one hand and the division of labour in journalism on the other, reveals the effects of professionnal hierarchies on the way the scandal was treated by the press. The form taken by this affair derives substantially from the way in which medical information is treated. Medical information has lost its relatively exceptional status, which is less and less medicalised and more and more competitive. This study shows also that journalistic activity is today less subject to the logic of politics than it is to that of two other logics : those of journalistic value -as recognized by journalists- and of the market, which become ever closer. The third part shows the growing effect that the journalistic field has on the ordinary working of other relatively autonomous social worlds such as the judicical sphere, when it imposes for example a form of " popular justice ".
