BACKGROUND and METHOD: The purpose of this study was to compare titers of cold agglutinins in schizophrenic patients with those in patients with major affective disorders and in normal healthy subjects. One hundred sixty-six psychiatric patients and 37 healthy comparison subjects were included in the study. Ninety of the patients suffered from schizophrenia, 54 from bipolar disorder, and 22 from major depression. Venous blood samples were obtained from all subjects between 8:00 and 10:00 a.m. and were immediately tested for cold agglutinin titers. RESULTS: A high frequency (42.2%) of positive cold agglutinin titers was detected in the schizophrenic patients, compared with the bipolar (11.1%) and unipolar (9.0%) patients and the comparison group (8.1%). The investigators did not find any pharmacological effect on these results. CONCLUSIONS: The findings suggest that, at least in this group, positive cold agglutinin titers are associated with schizophrenia. However, this observation cannot provide direct evidence for the involvement of viral or autoimmune factors in schizophrenia.Abstract Teaser