Iron deficiency can have nonhematological manifestations, some of which may affect the gastrointestinal tract. The aim of this study was to determine if iron-deficiency anemia in growing rats affected small-bowel permeability as assessed by the urinary ratio of lactulose and mannitol. Thirty-seven male Harlan Sprague-Dawley rats (21 d of age) were randomly divided into two groups and fed either an iron-deficient (n=19) or an iron-sufficient diet (n=18) that contained either 13.5 or 43.8 mg of iron/kg diet, respectively. Animals were evaluated between 25 and 38 d of dietary treatment. Intestinal permeability was assessed by measuring the lactulose/mannitol urinary ratio following administration of a solution that contained the two sugars. At the end of the study, the mean body weight of rats fed the low-iron diet was approx 95% that of the controls. The mean hemoglobin (g/dL) was significantly lower in the low-iron diet group (11.2+/-1.4) than in the control group (16.9+/-0.8) (p=0.001). The liver iron concentration (microg/g) of the anemic group (41.4+/-4.7) was also statistically (p=0.001) lower than in the control group (116.6+/-18.2). The lactulose/mannitol ratio was lower in the anemic rats (2.0+/-0.7) than in the control group (2.6+/-0.7) (p=0.008), a finding that is not suggestive of intestinal mucosal atrophy, previously described in anemic children.