Opening Paragraph: In this paper I consider some Lugbara notions about witches, ghosts, and other agents who bring sickness to human beings. I do not discuss the relationship of these notions, and the behaviour associated with them, to the social structure. The two aspects, ideological and structural, are intimately connected, but it is possible to discuss them separately: on the one hand, to present the ideology as a system consistent within itself and, on the other, to show the way in which it is part of the total social system. Here I attempt only the former.