SPECIF-X is the name of a tool developped by IGL to support the SADT methodology. This paper provides a very brief overview of SADT. It then presents the various features of the tool, seen at three functional levels: a production level, an organisation level, and an exploitation level. The paper then describes SPECIF's implementation, from a user's viewpoint. It discusses the impact of some constraints during the requirements analysis phase. It concludes by commenting upon the feedbacks already available from the first users, most of them coming from projects that were performed in 1985 and 1986 at SAT Control, for satellites. They show, on the one hand, that the use of the tool facilitates the introduction and the practical use of SADT, and, on the other hand, that it boosts both the quality of the functional requirements and the analyst's productivity. The paper also indicates the directions in which this product is being extended.