In order to determine the relative capacity for bowel adaptation in young versus older rats, 60% bowel resections were performed in seven 3-week-old and seven 8-week-old rats. These animals were then pair-fed with control animals that had undergone sham operations, and after 2 weeks, all animals were killed. Segments of remaining jejunum, midileum, and distal ileum were removed, and mucosa was scraped free using a glass slide. Mucosal wet weight, protein, RNA, DNA, and sucrase content were measured. Data were expressed as percent increase of each mucosal parameter in resected as opposed to control animals, and the two age groups were compared by unpaired t test. When data were examined per centimeter of bowel, increases in all parameters in each segment were substantially greater in the older animals, suggesting that older animals have a greater capacity for mucosal adaptation following massive bowel resection than do young animals. These findings correlate well with clinical experience which suggests that infants with massive bowel resection may require years of parenteral nutrition before total enteral nutrition is possible.