A comparative study of blood serum concentrations and pathogenic properties of circulating immune complexes (CIC), along with identification of their protein composition, was conducted in 45 patients with schizophrenia, 15 their healthy relatives and 39 normal controls. In patients and their relatives, mean concentration of small CIC was within the normal range, while concentrations of giant, large and middle CIC were higher than those of the controls (p<0.001). Over 80% of schizophrenic patients and their relatives had pathogenic immune complexes in the circulation. Clinical and immunologic analysis of patients with schizophrenia revealed a correlation between the illness duration and CIC concentration for all sizes. Smokers had significantly lower levels of small CIC comparing to non-smokers. Determination of CIC composition in patients and relatives revealed a presence of specific proteins in the immune complexes with molecular weights of 36 and 25 kDa. The results suggest genetic determination of autoimmune processes in schizophrenia.