Low melatonin and elevated cortisol levels have typically been reported during depression. The evidence that the converse is true during mania has been less well documented. In a single case design, repeated measures of nocturnal melatonin and cortisol were taken during mania, depression, and euthymia. Elevated levels of melatonin during mania and elevated cortisol levels during depression were the principal findings. There also did not appear to be any marked change in circadian rhythm of hormone output during the three clinical states. The implications of these findings in relation to noradrenergic dysfunction are discussed.