A system is described which adds simulated emotion effects to synthetic speech. The control parameters of a speech synthesizer are controlled by rule in order to simulate the features of emotion expressed in the human voice. The system can simulate six vocal emotions and was evaluated with naïve listeners. The results indicated that the system was producing recognizable vocal emotions, with perception rankings similar to those found by previous research on human emotional speech. This system has been developed for use in voice prosthesis systems for non-vocal disabled persons, although it could be used to enhance any application which uses rule-based synthetic speech.