A distinctive pattern of clinical change during eight affective episodes is reported in a rapidly cycling manic-depressive patient. After a rapid switch to near maximal intensity of affective symptoms, slow changes in symptomatology were documented by significant slopes and correlation coefficients over the course of each episode. Decreases in depression, anxiety, drowsiness, helplessness/hopelessness, anger, and sadness preceded the switches into mania; decreases in mania, euphoria, seeking others, and talking preceded the switches into depression. Psychologically important events appeared to regularly precede rapid mood switches. It is suggested that the consistent, slow clinical changes which occur during affective episodes may reflect part of an underlying rhythmic biological process and that environmental events may be capable of triggering a final common pathway for the mood switch during a vulnerable period.