The expanding field of stem cell research is now beginning to help with the problems of modern psychiatry. On the one hand, induced pluripotent stem cells (iPSCs) can now be used to generate neural cell lines from patients suffering from psychiatric disorders, which can then serve as models for studying changes in gene expression pattern involved in the pathogenesis of these diseases. These artificially generated neural cells are also employed in studying the efficacy of newly developed antipsychotic treatments. On the other hand, evidence has accumulated that not only monocytes, which can be microglia precursors, but also certain other adult bone marrow-derived cells may cross the blood–brain barrier and affect biological processes in brain tissue. Along with evidence of circulating and brain-infiltrating cells, there are well-studied factors (e.g., chemokines, phosphosphingolipids, and complement-cleavage fragments) that modulate trafficking of these cells between bone marrow and neural tissue. These observations may help to shed new light on the pathogenesis of psychotic disorders and, in the future, perhaps help to develop more effective treatments.