Recent gene-expression findings may energize the search for a mechanism in bipolar disorder pathology. Chris-tine Konradi and collaborators, from McLean Hospital, Belmont, Mass., and Harvard Medical School, showed that of 43 genes downregulated in brain specimens from subjects with bipolar disorder, 18 encode mitochondrial proteins.[1] These results bolster a hypothesis put forth almost four years ago by Tadafumi Kato, currently at the RIKEN Brain Research Institute in Japan. Mitochondrial dysfunction, he proposed, would explain the abnormal energy metabolism detectable in bipolar brains and could comprehensively account for the patho-physiology of the disorder.[2]