The paper revies briefly the principles which should guide the development of automated psychological test systems. These are illustrated by reference to research and development studies undertaken with the Perceptual Maze Test. Building computer models of the way in which subjects might tackle problems can be a fruitful approach to research on human skills. The Perceptual Maze Test is particularly suited to the development of such simulation studies. The possible role of these tests in assessing treatment effects in neurology and psychiatry is discussed and an example of this type of application is presented.