The paper aims at illustrating the phonetic transcription rules implemented in a text-to-speech synthesis system of Italian. The development system employed for rule writing is presented first. The system makes it possible to process linguistic information at various levels, using a conventional context-dependent format. The rule set, made up of graphemic, phonetic and word boundary rules, is then described. Transcription rules furnish a reasonable solution to [s, z], [ts, dz], [‘e, ‘ε], [‘o, ‘o], [i, j, i] and [u, w, i] phone distributions, as used in Northern Italian pronunciation. Statistical evaluation of the transcriber performance was carried out on a significant corpus of words with encouraging results: 93.1 % correct transc