Anxiety and plasma cortisol at the crest of the circadian cycle:reappraisal of a classical hypothesis.

Near-maximal anxiety by subjective and behavioral criteria was evoked and terminated in phobic patients by initiation and termination of rapid live confrontation ("flooding in vivo") with the specific stimulus that each avoided, at a time approximating the crest of the circadian cycle of adrenal cortical function. The procedure was associated with moderate, but not marked, elevations of plasma cortisol above control levels in some, but not all, subjects. Differences in anxiety levels as self-rated by the patients did not account for differences in cortisol response. The findings should stimulate further reevaluation of the hypothesis that affective arousal is the key psychological determinant of adrenal cortical function. Dissociation between subjective-behavioral arousal and plasma cortisol during flooding may be a manifestation of what behavior therapists call "desynchrony of fear."