Northern Territory Aboriginal children hospitalised with acute gastroenteritis have high rates of acidosis, hypokalaemia, and dehydration. To determine whether Aboriginal children with and without diarrhoea have greater impairment in intestinal function than non-Aboriginal children, as assessed by increased permeability ratios. A descriptive study of 124 children (96 Aboriginal and 28 non-Aboriginal) hospitalised with and without diarrhoea. Intestinal permeability was assessed by the lactulose to rhamnose (L-R) ratio from a five hour urine collection. In Aboriginal children, mean L-R ratios (95% confidence intervals) were 18.3 (17.1 to 19.6) with diarrhoea and 9.0 (7.3 to 11.0) without diarrhoea, and in non-Aboriginal children they were 5.9 (2.8 to 12. 3) and 4.2 (3.3 to 5.2), respectively. In patients with diarrhoea, L-R ratios were significantly raised when accompanied by acidosis (mean, 22.8; 95% CI, 17.0 to 30.5), hypokalaemia (mean, 20.7; 95% CI, 15.4 to 27.9), and >/= 5% dehydration (mean, 24.3; 95% CI, 19.0 to 29.6) compared with none of these complications (mean, 7.0; 95% CI, 3.5 to 13.8). The high incidence of acidosis, hypokalaemia, and dehydration in Aboriginal children admitted with diarrhoeal disease is related to underlying small intestinal mucosal damage.