The Isakower phenomenon is a situation in which an individual typically experiences perceptions of enlargement or thickening, altered states of consciousness, sensations of floating, and impressions of the emergence and disappearance of an oral mass. This paper defines the phenomenon, reviews the literature, and describes a case in which a patient experienced it. The patient manifested the phenomenon symptomatically in the aftermath of a toxic state, and the elements were analysed for several years. There was support for Isakower's original thesis that the regressive states serve to defend against threatening incestuous fantasies. However, the Isakower phenomenon in this patient was the result of a multiplicity of determinants, largely defensive, involving many developmental levels.