This paper presents a ten months long experiment led at TRANSPAC to check the interest of a Formal Description Technique like Estelle for industrial purposes. Through the Intelligent Network new service introduction, Estelle-and associated tools, e.g. VEDA and EC H ID N A-has been used for different purposes: validation of a brand new protocol and test of its implementation, modelisation of an already existing one, and validation of the integration of both protocols. After a brief introduction to the TRANSPAC framework, we present an outline of these experiments. Then we draw some conclusion on the suitability of both Estelle and the tools used in this context, and on the economical balance of such an approach to deal with concrete problems.