This paper sets out possible links between disruption of circadian rhythms in bipolar disorder and the affective symptom, which are experienced in this disorder. Evidence is drawn from Healy and Williams' [Psychiatr. Dev. 1 (1989) 49.] review of circadian function in manic depression, along with later reports, which indicate a role for disrupted circadian rhythms in both depressed and manic phases of manic depression (bipolar disorder). This is integrated within a version of the multilevel model of emotion proposed by Power and Dalgleish [Cognition and emotion: from order to disorder. Hove: Psychology Press (1997); Behav. Cognit. Psychother. 27 (1999) 129.]. The aim of this process is to propose a possible psychological mechanism by which the disruption of circadian rhythms might result in the observed clinical symptoms of bipolar disorder. The integration of these approaches leads to a number of specific testable hypotheses that are relevant to future research into the psychological treatment and understanding of bipolar disorder.