We compared the in vivo transport of zinc in segments of jejunum, ileum, and colon of 2-week-old (suckling) and 6-week-old (adolescent) rats. In normal rats, net absorption and lumen to mucosa flux of zinc, normalized for differences in size of the intestine (mumol/h/g dry weight) were significantly greater in all perfused segments of the suckling compared with corresponding segments of the adolescent rats (p less than 0.05). Moreover, zinc transport rates in colonic segments of the suckling rats were significantly greater than corresponding transport rates in the small intestinal segments (p less than 0.05). In the adolescent rats, transport rates in the colonic segments were similar to corresponding rates in the small intestinal segments. Growth retardation (pups raised with mothers fed a diet deficient in protein) appeared to have no effect on net absorption or lumen to mucosa flux of zinc in suckling rats, but significantly enhanced net absorption and lumen to mucosa flux of zinc in the adolescent rats.