Schizophrenia has many clinical expressions and probably different etiologic factors. Infections, autoimmune mechanism and related neurodevelopmental abnormalities have been suggested as possible etiologic factors of schizophrenia. It has been reported that immunoreactivity to heat shock proteins, which play a protective role against environmental stresses in a cell, might be related to the pathogenesis of schizophrenia. Therefore, we examined the immunoreactivity to heat shock protein 70kDa and 90kDa(HSP70 and 90) in 91 patients with schizophrenia and 83 normal controls. Ig G antibodies to HSP70 and 90 of sera were quantitated by ELISA. The optical density(OD) was measured by an automated microplate reader at a wavelength of 490nm. The amounts of antibodies to HSPs were expressed as arbitrary units(AU)/ml related to a standard serum. The limit for elevated antibody titers(anti-HSPs positive or negative) was set at two standard deviations added to the mean of the normal controls. Twenty nine(31.9%) of the 91 patients showed anti-HSP70 positive and 19(20.9%) of those showed anti-HSP90 positive. On the other hand, only 1(1.4%) of the normal controls and 4(4.8%) of those showed anti-HSP70 positive and anti-HSP90 positive, respectively. The titers of anti-HSP70 positive were related with BPRS scores, while those of anti-HSP90 positive were not. There were no relationship between antibody titers and clinical variables including age at onset, duration of illness, family history of schizophrenia or number of admission. The titers of anti-HSP70 positive were significantly associated with anti-HSP90 positive. Our results suggest the presence of abnormal immune reactivity involving HSP70 and HSP90 in a subset of patients with schizophrenia.