In this paper we study the effect of source changes, caused by vocal tract load, in perception of nasality. For that we have developed an articulatory speech synthesizer, includ-ing a comprehensive nasal tract model and an interactive glottal source model. Our main objective was to inves-tigate to what extent is necessary, in systems aimed to produce high quality synthetic sounds, to include the ef-fect of source-tract interaction in the glottal source model when synthesizing nasal vowels. In our studies we used Portuguese nasal vowels. Portuguese uses nasalization of vowels in its phonological inventory. Changes in glottal wave, caused by the additional load of the nasal tract are more significant in vowels like [i] with low F1 and high F2 . Effects are more dramatic in time rather frequency domain. Perception tests favor the idea that listener arent able to detect the perceptual effect of source-tract inter-action changes caused by the additional coupling of the nasal tract. More tests are needed to support, or reject, this.