This paper reports a temporal analysis of stressful events, behavioral ratings and corticosteroid determinations during periods of psychotic depressive crisis. The investigation is part of a continuing research program at the National Institute of Mental Health on the biochemical and behavioral aspects of depression. It is suggested that the depressive crisis is an important segment of extreme human behavior and that as a time of change, it offers a tool for understanding depressive illness.1. A behavioral observational system was developed, making it possible to measure reliably depression and psychotic behavior on a continuous longitudinal basis in depressed hospitalized patients and to quantitatively describe crisis periods.2. The question as to the sequence of endocrine or behavioral changes was considered and it was shown that both the urinary 17-hydroxycorticosteroids (17-OHCS) changes and the behavioral changes occurred on the same day rather than one preceding the other by a day or more.3. A day characterized by behavioral and biochemical changes was identified and labeled, "the crisis onset day." Behavioral ratings and hormonal values on this day differentiated it from previous days during the patient's hospitalization, in terms of the intensity of observed response. These changes in the organism suggest the utility of using this day as a focus for the study of environmental precipitating factors.A period of increased environmental stress existed for an average of 13 days prior to the crisis day. The events tended to build up during this period so that on the crisis onset day there was an average of four stressful events occurring concomitantly. At least one event occurred prominently in each case on the crisis day.4. Three aspects of psychological threat were identified for these stressful events. They were: a) An environmental challenge to the patient's concept of his own mental health; b) a loss of ego support; c) involvement of a central conflict area. These events share in common the forcing into awareness of denied thoughts, conflicts and feelings.5. The crisis onset days in the first 5 cases were characterized, biochemically, by a substantial increase in 17-OHCS levels and behaviorally by an intense awareness of and struggle with ego alien material, which was depressive in nature and by the onset of at least one new symptom indicating the breakdown of ego defenses.Abstract Teaser