An opportunity occurred during an analysis to follow the reappearance of a specific infantile wish, long ago repressed into the unconscious. The analytic situation (free association, slips, behaviour in the transference, dream interpretation) made it possible to observe the modifications this instinctual wish had to undergo in each case before the ego permitted expression (i.e., what defence mechanisms the ego brought into action during sleep and wakefulness under the specific situation of analysis), and how a compromise was reached in a neurotic conflict between instinctual expression, superego, and the ego The nature of the situation permitted an attempt at reproduction to reaffirm the basic tenets of psycho-analytic theory regarding mental functioning.