In this study, we demonstrate that embryonic stem cells can be engineered to differentiate into high percentages of serotonergic and dopaminergic neurons. In vitro, these cells release serotonin and dopamine in response to membrane depolarization. Upon engraftment into the medial prefrontal cortex in rats, the homolog of the human anterior cingulate cortex, the cells assumed neuronal morphologies, expressed monoaminergic-specific proteins, and seemed to functionally integrate, as assessed by the upregulation of the immediate-early gene, cfos. Furthermore, the transplanted animals performed in a manner similar to that of animals that received the antidepressant, citalopram, when administered the forced swim test, a validated model of human depression. These results suggest that transplantation of customized stem cells might perhaps be useful in the study treatment of psychiatric disorders.