AbstractImmune complexes may be important in the pathogenesis of the liver disease associated with idiopathic ulcerative colitis. In the present study, we documented Fc receptor‐mediated clearance by the reticuloendothelial system of immune complex‐like material from the systemic circulation of 25 healthy control subjects, 19 patients with ulcerative colitis alone, 9 patients with ulcerative colitis and elevated liver enzyme tests and 8 patients with various other formsof chronic liver disease. Following an intravenous infusion of IgG‐tagged51Cr‐labeled autologous erythrocytes, serial blood samples were drawn over a 2‐hr period of time, and computer‐generated clearance curves were obtained. The time required for clearance of 50% of infused erythrocytes (T1/2) was then calculated. Serum immunoglobulin (IgA, IgG and IgM), complement (C3 and C4) and immune complex‐like activity (IgG and IgM types) were also determined. Sixteen of 19 (84%) ulcerative colitis patients and 7 of 8 (88%) chronic liver disease patients had normal clearance T1/2's (when compared to 25 healthy controls). Conversely, only 1 of 9 (11%) ulcerative colitis + chronic liver disease patients demonstrated normal clearance function. Aside from serum IgM levels, the results of serum immunoglobulin, complement and immune complex‐like determinations were similar in ulcerative colitis and ulcerative colitis + chronic liver disease patients. Serum IgM levels, however, were significantly decreased in ulcerative colitis patients and increased in ulcerative colitis + chronic liver disease patients (p<0.001).These results indicate that the reticuloendothelial system of patients with ulcerative colitis and chronic liver disease is impaired in its ability to clear immune complex‐like material from the systemic circulation. This finding tendsto support the hypothesis that immune complexes are of pathogenic importance in the liver disease associated with idiopathic u