Exorcism may well be the foundation stone of the Chinese religious edifice. Conceived, for over two thousand years already, as a kind of judicial interrogation, it is related both to the shamanism of antiquity and to the theatre. The present study of an exorcism performed in November 1984 by northern Taiwanese Taoists seeks to demonstrate that the fundamental technique of this ritual is that of symbolic transformation: for each individual rite there is an immortal who, once he has been invoked, causes the desired transformation and thus enables the priest to execute the rite efficaciously.