Small intestinal permeability to mannitol and lactulose was studied in healthy English and apparently healthy Sudanese subjects to determine whether any differences were apparent. Permeability was assessed by measuring urinary recovery of the test substances after oral ingestion. The mean excretion of lactulose was significantly higher and the mean excretion of mannitol was significantly lower in the Sudanese than in the English subjects. Lactulose to mannitol excretion ratios were significantly higher in the Sudanese. These data demonstrate abnormal intestinal permeability in the Sudanese subjects and indicate the presence of an asymptomatic enteropathy.