There has been considerable controversy over the correct diagnosis for patients with mood disorder associated with the lifetime occurrence of hypomanic symptoms which are sub-threshold for the diagnosis of bipolar disorder. Extrapolating from the accelerating accumulation of knowledge of the biology of psychiatric disorders over the last several decades, it is easy to anticipate that this trend will continue and that such knowledge will define the molecular pathways whereby genes and environment affect the risk for mood disorders. There are early efforts to apply proteomic methods to mood disorders. Electrophysiology, primarily in the form of electroencephalographic recording, has shown significant promise in application to mood disorder therapeutics. An important intellectual trend is that the rapidly advancing technologies of quantitative neuroscience and molecular genetics appear to be making enormous progress toward demonstrating a neurobiological substrate of mood disorder.