De Donà Giorgio**, Rendina Romeo**, Pirovano Giovanni*, Valagussa Claudio* ICOLIM 2006, 8th International Conference on Live Maintenance Praga, 7-9 Giugno 2006 *CESI RICERCA **Terna SpA During the last decades the use of composite insulators has grown all over the world. These insulators have advantages from both structural and operational points of view. Diagnostic techniques for these insulators have been studied and developed during the last years. However, in LLM (Live Line Maintenance) international standard, the procedures and distances to adopt for composite insulators have not yet been defined. This paper, after reporting some data on the characteristics and diffusion of composite insulators, describes the diagnostic techniques available for the assessment of their conditions, with particular reference to laboratory activities carried out in Italy. With reference to these experimental activities, indications are given about in field applications. Particular attention is given to electric field measurement, operation that need to be carried out by LLM techniques. Description is given of the future activities that TERNA and CESI RICERCA intend to carry in order to deepen the argument; a common effort at international level is also encouraged in order to overcome the present lack of standard for LLM in presence of composite insulators.