This paper presents a phoneme/diphone based speech synthesis system for the (Brazilian) Portuguese language. The basic idea bearing this system is the construction of a library of phonetic units, and processing of those basic units to build an utterance. The system is complemented by a text to phoneme translator described in [Cam95]. The phoneme's representation in the library is based on a linear prediction model; the filter which models the vocal tract is represented by Line Spectrum pairs, and the excitation by Code Excited Linear Prediction (CELP) parameters. Thus paper is organized as follows. After a brief introduction, CELP coding is briefly presented in part 2. Part 3 presents the relevant points to be applied in speech synthesis. Part 4 and 5 constitutes the main contribution of this paper, detailing the process of building the phoneme library and the interpolation techniques used. part 6 presents some concluding remarks.