This investigation was undertaken to determine the effects of purified cellulose and xylan on the apparent absorption and tissue concentration of zinc and copper in male weanling Sprague-Dawley rats. The control group was fed a fiber-free diet and six other groups were fed a diet containing 3, 6 and 12% cellulose or xylan. All diets contained 10 ppm Zn and 4 ppm Cu. Four 14-d collections of feces were made during wk 3 and 4, 10 and 11, 17 and 18 and 24 and 25. The balance technique was used to measure the apparent absorption of zinc and copper. After 26 wk of consuming the test diets, rats were killed and plasma liver, kidney and mucosa analyzed. There were no significant differences between groups in regard to weight gain, feed intake and feed efficiency. The average amounts of ingested cellulose and xylan that survived the passage of the intestinal tract were 86 and 18%, respectively. Inclusion of 12% cellulose in the diet resulted in a significantly lower apparent absorption of both zinc and copper, whereas at 6% cellulose only the absorption of zinc was lower. The addition of cellulose also resulted in lower plasma zinc and liver and kidney copper concentrations. In contrast to cellulose, xylan did not exert a significant influence on apparent absorption and tissue concentrations of the minerals. Regardless of the type and level of fiber, the apparent absorption of zinc and copper declined as rats grew older.