We report two patients with psychotic depression who were successfully treated with a lithium addition to ongoing paroxetine treatment. In both cases, plasma brain-derived neurotrophic factor (BDNF) levels increased about 2-fold after lithium augmentation to paroxetine, compared with paroxetine treatment alone. Plasma paroxetine levels did not change after lithium addition. These results suggest that the increases in plasma BDNF levels reflect recovery from depressive symptoms in psychotic depression.