Any attempt to define the notion of "mysticism' must face the challenge presented by the evanescent nature of its object. The scholars must rely on written texts or other reports without personal experience, but the mytics, as well, are limited by their cultural background; trying to share an experience that lies beyond the words, they have to formulate it within a system of notions as known in their own religion. Among the religious trends of Antiquity the Neoplatonic theurgy bears the closest resemblance to something we can rightly call mysticism. As a result of the theological background of the post-Iamblichean theurgy the paradigmatic form of mystical experience became the divine possession of a medium, so the theurgist himself remained a mere observer. In the final chapters I make an attempt to identify signs of genuine mystical experience in the Chaldean Oracles, a key-text of the Neoplatonic theurgy.