The first effort was made to document that elemental diet was satisfactory in maintaining normal growth in rats. A second effort was made to determine the maximum resectability of the intestine when rats were fed only by the elemental diet. These experiments were done in 80 ten-week-old female Wister rats. Results obtained are as follows (1) Eight rats fed only by the elemental diet through gastrostomy for 20 days gained more weight than pre-operative weight (P<0.02), and a positive nitrogen balance was obtained when rats were given with calories of 303 cal/kg/day and 8.25g/kg/day of amino acids. Also long term experiment of giving the elemental diet by mouth for 60 days resulted in increase of body weight (P<0.001), and there was no abnormality in hematological and pathological evaluations. (2) Body weight became heavier than that of before operation in the rats with 70% or 80% resection of the small intestine with P<0.001 and P<0.05, respectively. In the latter group, however, recovery from surgical assault were delayed, the pancreas and lung were often compromised and blood urea nitrogen as well as serum enzymes such as s-GOT and s-GPT were abnormally high. In 90% resection rats mortality was very high (85.7%). Therefore, it was concluded that the maximum resectality of the small intestine was 70% when rats were fed by elemental diet. (3) If the ileocecal valve was resected, pre-operative body weight was not resumed even in 70% -resection rats, indicating the importance of the valve. (4) When pyloroplasty was added in 70% -resection rats, gain in body weight was larger as compared with 70% resection group and non-resection group (P<0.005 and P<0.01, respectively). Abnormal findings in the liver, pancreas and lung were lesser and serum protein was elevated (P<0.001). These results show that elemental diet is effective tool of nutrition and exclusion of small intestine can be done safely as much as 70% However, improvement of administration and nutritional constitution may be able to endure much more extensive resection.