Immune complexes in the choroid plexus in liver cirrhosis. A histopathologic and immunofluorescence study of the choroid plexus was performed in 12 cases of liver cirrhosis (cirrhosis group) and in 20 patients who died of diseases with no evidence of liver or brain involvement, and in which renal disease and alcoholism were also excluded (control group). IgA, IgG, IgM, C3, and C1q were investigated by direct immunofluorescence technique. Positive immunofluorescence in the choroid plexus was found in 83.33% of the cirrhosis group. IgA and IgG were the immunoglobulins more frequently found. C3 was also commonly found. Histologic examination of the choroid plexus showed changes in 66.67% of the cirrhosis group characterized, mainly, by subepithelial deposition of a homogeneous, acidophilic, and periodic acid-Schiff-positive substance, with thickening of the epithelial basement membrane. In the control group, the immunofluorescence in the choroid plexus was negative in all cases and only two cases (10%) presented histopathologic changes of the choroid plexus with a pattern similar to that of the cirrhosis group. 