The activity of specification is becoming considerable; every day an enormous quantity of pages which, for the most part, is written in natural language. For CNET, which carries out studies of the services and equipment of France Telecom and which has the capability of putting into practice the stages of specification and validation, the need to reduce the time needed in the development of the services is a priority. One method towards achieving this objective is to formalise the maximum number of specifications received. With this in mind, we will try to demonstrate the possibility of a certain automation in the passage from the informal to the formal, by means of methods and proven tools, available to assist an expert in specifications. For this end we propose a process of formalisation which relies on an intermediary representation of the specifications with the formalism of conceptual graphs before arriving at a formal description in Z of the initial spécification.