85% enterectomy or jejunal biopsy was randomly carried out on 80 male Sprague-Dawley rats, 300-350 gm. After recovery, rats in each group were randomly fed either elemental diet (ED) or rat chow. All rats were sacrificed 8 weeks postoperatively. Biopsied rats gained more weight with ED than chow (22% vs. 18%; p less than .01). Resection produced greater weight loss than biopsy (p less than .01) and slower gain (p less than .01). The failure to gain was most marked in ED rats, significantly less than in the chow group (p less than .05) by week two. A fall in hemoglobin, protein and albumin was seen: neither the fall nor difference between the groups was significant (p greater than .05). Enterectomized chow rats ate 22% more than their controls (p greater than .05). Increase in bowel length after resection, equally divided between jejunum and ileum, was 21% with ED and 26% with chow. Gut diameter after resection increased 104% and 98% with chow and ED, respectively. Villus height increased 65% in the jejunum of both enterectomized groups and 85% and 78% with chow and ED, respectively, in the ileum. Changes in gut length, diameter and villus height are significant in each group (p less than .01) but not between groups (p greater than .05).