DNA and RNA content and the timing of development of various histological features in the small and large intestine of in-pouch tammar wallabies (Macropus eugenii eugenii) of various ages were measured. A significant decline in gut tissue DNA concentrations and increase in the RNA/DNA ratios over 300 days postpartum indicated that the early postnatal increase in gut tissue mass resulted largely from hypertrophy. Mean duodenal and ileal villus height and crypt depth were significantly greater for in-pouch young aged >100 days compared with those <100 days and were significantly greater in the duodenum than in the ileum. Goblet cells appeared more slowly during development and were fewer in number in the duodenal than in the colonic mucosa. The numbers of mucin-secreting duodenal goblet cells were greater in pouch young aged >100 days than in young aged <100 days. The colonic mucosa exhibited no villi or villus-like folds. Colonic crypt depth increased uniformly with age.