In patients with schizophrenia, the levels of T-helper (Th-) 1-specific IFN-γ and TNF-α, and Th2-related IL-6 were significantly higher in the plasma of the schizophrenic group (n = 71) compared to controls (n = 174) while mean plasma tryptophan concentration of the schizophrenic patients was significantly lower in contrast with controls. This evidence concerns the gene TNF and schizophrenia.