Forty male rats (126 g body weight) consisting of four rats a group were housed and rats of each group were given a treatment diets containing cellulose, rice-bran fiber, spinach fiber, burdock fiber, cabbage fiber, soybean fiber, Japanese-radish fiber, carrot fiber and corn fiber for five days. The remaining four rats were fed a non-fiber diet as controls. The animals were orally administered with 0.5 ml of the rice-bran oil used by Yusho patients and kept on the same diets for five days. The rice-bran oil was contaminated with 2, 3, 7, 8-tetrachlorodibenzofuran (2, 3, 7, 8-T4CDF, 458.7 ng/ml), 2, 3, 4, 7, 8-pentachlorodibenzofuran (2, 3, 4, 7, 8-P5CDF, 802.4 ng/ml) and 1, 2, 3, 4, 7, 8-hexachlorodibenzofuran (1, 2, 3, 4, 7, 8-H6CDF, 752.3 ng/ml). PCDF in feces and liver were analyzed by high resolution gas chromatography-mass spectrometry. The fecal excretion of 2, 3, 7, 8-T4CDF in the group fed rice-bran fiber and spinach fiber was significantly (p < 0.01) stimulated 11.3 and 6.8 times, respectively, as compared with controls. Moreover, 2, 3, 4, 7, 8-P5CDF and 1, 2, 3, 4, 7, 8-H6CDF were excreted in stool at the rate of 4.1 and 3.4 times, respectively and 2.1 and 2.2 times, respectively, as compared with controls. These results suggest that administration of dietary fiber is useful for a new approach to therapy of Yusho patients.