In this pilot study, we propose to characterize the pattern of activation of the kynurenine pathway of tryptophan metabolism in peripheral macrophages of patients with schizophrenia. To do this, we will measure the gene expression of several major enzymes in this pathway in macrophages, including the key enzyme involved in tryptophan to kynurenine metabolism, IDO, by means of quantitative reverse-transcription polymerase chain reaction (RT-PCR). The focus on enzyme mRNA expression as opposed to serum or cerebrospinal fluid levels of metabolites provides a possibly more sensitive characterization of the activation of this metabolic pathway.