From a cycling standpoint, "circular insanity" (Falret) and "dual-form insanity" (Baillarger), both described in hospital patients in 1854, are at the severe end of the spectrum of what we now call "bipolar disorders". Falret was prescient in suggesting that circular insanity was rare in the community, where depressive cycles are prevalent. These disorders are now respectively referred to as the "hard" (manic-depressive) and "soft" (bipolar spectrum) phenotypes of the disorder. This paper focuses on the latter, more prevalent depressive expressions of the spectrum, which share with the manic and circular forms a lifelong tendency to recur. Their cyclicity may involve putative "clock genes". The genetics of psychotic mania overlaps somewhat with the genetics of schizophrenia. As regards depressive recurrence, putative genetic factors have been identified, including a polymorphism of the serotonin transporter, which significantly increases the subject's vulnerability to stress; a mediating pathogenetic variable appears to be temperamental dysregulation (e.g. neuroticism and cyclothymic lability), which produces hyperemotional reactivity to such stressors. The growing recognition that many depressive recurrences belong to a broad spectrum, affecting 5-10% of the population, represents a new public health challenge. Although the new class of serotoninergic antidepressants offer a practical approach to the management of depressive episodes, further research is needed to determine the point of the spectrum at which mood-stabilizing therapy should be started--and in what combinations--in order to prevent recurrence and suicide.