Depression, hypomania, and depersonalization in a girl of twenty-three are described and interpreted as major related elements in a pattern of defense. The hypomanic episodes, which were less frequent and severe than her depressive symptoms and feelings of unreality, were a defense by denial. Such a defense appears clinically as impairment of perceptual and reality testing functions of the ego. Depersonalization seemed to be an emergency defense against the threatened eruption into consciousness of a massive complex of feelings of deprivation, rage, and anxiety. The data suggested moreover that depersonalization was called into play when the hypomanic defense failed to keep dangerous affects in repression. An attempt is made to correlate the symptoms selected for special study with the patient's other prominent symptoms and character

traits, notably her severe masochism and sleep-waking disturbance, and with the phenomena of normal sleep.