The clinical features of bipolar disorders can be correlated with responses to medications. Patients who respond to lithium, for example, often present differently from those who respond to divalproex or carbamazepine, but the correlations are relatively modest. Brain-imaging tools, such as positron emission tomography (PET), single photon emission computed tomography (SPECT), and functional magnetic resonance imaging (fMRI), can relate brain function to clinical features and medication responses. For example, in depression, it appears that prefrontal cortical function is decreased while subcortical anterior paralimbic activity is increased. Preliminary evidence suggests that baseline metabolism increases and decreases in the left insula may be associated with carbamazepine and nimodipine responses, respectively, and that cerebral lithium concentrations may correlate with antimanic effects. Although it is not yet a clinical tool for bipolar disorders, brain imaging provides useful research data to understand the fundamental neurobiology of mood disorders and to more effectively target therapeutics.