The first part of this paper presents an extension of Osgood’s Mediation Theory to symbolic phenomena: It was hoped that use of learning theory principles would allow a redefinition of terms and the formulation of psychoanalytic hypotheses pertaining to symbolism in a form testable by experimentation. The second part involves an extension of this theory to several specific experimental studies in which hypnosis was used as the primary method of investigation and the semantic differential as the principal measuring instrument. Particular interest was focused on the assumed disguise function of dream symbolism. All of the studies reported represent an effort toward identification and clarification of the psychological laws underlying the acquisition and modification of sign significance involved in the process of symbolization.