We examined serum interleukin-6 (IL-6) in 90 schizophrenic patients in remission and 90 normal controls using enzyme-linked immuno-sorbent assay (ELISA). We found a significant difference in variation between the schizophrenic and the control groups (F = 10.9, P less than .002). The difference in distribution was also statistically significant by Kolmogorov-Smirnov (chi-square = 45.0, P less than .001). Eight patients had aberrantly high serum levels of interleukin-6. Since the higher levels of IL-6 are characteristically found in several autoimmune disorders, our finding suggests a link between schizophrenia and immune response, which could be either autoimmune or a process induced by reactivation of viruses.