This essay discusses and illustrates the phenomenon of concretizing through acting out. It describes how acting out may express, in a concrete manner, traumatic experiences from the past–experiences from the lives of others who have denied these experiences, which are therefore not represented on the fantasy level. The concept is developed on the basis of the treatment of a young man who acted out in analysis violent destructive affects both against himself and the analyst. In this acting out, his identification with various roles of his persecuted family, which had been denied, found its expression. His psychotic episodes were shaped through his unconscious ambivalence toward his inner father-objects, whom he wanted at the same time to cure and to kill.