Text-to-speech systems usually consist of a preprocessor for expanding abbreviations, a system for converting orthographic text to a phonemic representation, rules for generating appropriate rhythm and intonation, and a speech synthesizer to generate an acoustic waveform from the phonemic representation. Multi-layer perceptrons have recently been used for the orthographic to phonemic conversion process. In this paper the possibility of using perceptrons in the preprocessor is explored. It is shown that single-layer perceptrons are sufficient for expanding 3-digit numbers, 4-digit numbers and cardinal numbers into appropriate orthographic text, but a multi-layer perceptron is required for expanding 12-hour clock times.