Within the next few years, there will be an extensive proliferation of various types of voice response devices in human-machine communication systems. Unfortunately, at present, relatively little basic or applied research has been carried out on the intelligibility, comprehension, and perceptual processing of synthetic speech produced by these devices. On the basis of our research, we identify five factors that must be considered in studying the perception of synthetic speech: (1) the specific demands imposed by a particular task, (2) the inherent limitations of the human information processing system, (3) the experience and training of the human listener, (4) the linguistic structure of the message set, and (5) the structure and quality of the speech signal.