The principle of homeostasis is applicable to psychological phenomena and analytic theory. The ego functions mediate stimuli in the service of homeostasis. Under stress, the ego improvises adaptive expedients for maintaining maximal organismic integrity. This regulatory function of the ego can be conceptualized in five hierarchically arranged groups representing increasingly great degrees of failure in integration. This way of representing the ego functions is in keeping with general organismic-biologic theory and facilitates more precise designation of process and stage in the development of illness.