Two hundred and forty commercial female day-old broiler chicks were used to investigate the effects of high-fiber grains on the growth rate and various gut sizes. Four experimental diets were formulated to have similar energy and protein contents, with corn and sorghum as low-fiber grains, and rye and hulled barley as high-fiber grains. Birds were housed randomly in 20 wire-floor cages. There were 5 replicates per treatment and 12 chicks per replicate (pen). At 3 wk of age, rye-fed broiler chicks grew at significantly lower rate than did the other birds. At 6 wk of age, the growth rates of birds fed rye and sorghum were significantly lower than those of birds fed barley and corn. The feed efficiency of the rye treatment at 6 wk of age was significantly poorer than those of corn and barley treatments, and that of the sorghum treatment was intermediate. The fiber levels in grains did not exert any consistent effect on the weights of liver, gizzard and pancreas of broilers at 6 wk.of age. However, the intestines of birds fed high fiber grains tended to be heavier and longer than those fed low fiber grains, and this trend was especially noticeable in rye-fed birds. The microscopic observation of deal and colonic tissue slides from 3-and 6-wk-old broiler chicks revealed no difference in diameter, villi length, and in the thickness of muscularis mucosae, circular muscle layer and longitudinal muscle layer. However, the diameter of colon in 6-wk-old rye-fed birds was significantly larger than those fed the other grains.