To investigate the therapeutic effects of rice bran fiber (30 g/day) and cholestyramine (12 g/day) for Yusho, clinical signs and symptoms, and laboratory examinations were studied before, during and after 14 day-treatment in four patients with Yusho. The increases of bowel movements and abdominal distention were observed in two of these patients, although no effect was seen in physical findings. In peripheral blood cells, red blood cell counts decreased significantly, from 430 +/- 47 x 10(4)/mm3 (mean +/- SD) to 378 +/- 48 x 10(4)/mm3 (p < 0.01) after therapy. Hemoglobin as well as hematocrit levels were also reduced significantly afer the therapy. However, no significant effect of the treatment was observed in white blood cell counts or platelet counts. In biochemical parameters, a significant depression was observed in total cholesterol levels after the therapy (from 262 +/- 31 mg/dl to 179 +/- 33 mg/dl; p < 0.005). A significant elevations was observed in serum levels of alanine aminotransferase and sodium, while significant depressions were found in serum levels of cholinesterase, total protein, albumin, gamma-globulin, and potassium.