Secondary hypotheses: Serum tryptophan levels will be lower in patients with schizophrenia compared to controls, and they will correlate with measures of dysphoria. Serum kynurenine levels will be elevated in patients with schizophrenia, particularly in deficit syndrome patients. mRNA expression levels of enzymes downstream from IDO will differ between patients and controls. Measures of immune activation will be influenced by medical disease burden (medical comorbidities).