 The application of high resolution 3D PET and MRI-based region-of-interest analysis will permit specific assessment of abnormalities of the D23 receptor system in currently depressed individuals with MDD and BD and of correlations with clinical ratings in ventral and dorsal striatum as well as in extrastriatal areas such as the amygdala, anterior cingulate cortex, medial prefrontal cortex and orbital cortex. Possible relationships of polymorphisms in the genes coding for elements of the dopaminergic system as well as the dopamine receptors being studied in MDD or BD with the level of binding detected will be investigated collecting preliminary data. 