A study is made of the behavior of urinary excretion of D-xilose three and five hours after the ingestion of 5 and 25 g of the substance. Twenty individuals were studied, 13 as control having no intestinal mucosa disease and 7 with steatorrhea and enteric lesions histologically confirmed. An analysis of the results revealed that with both doses it is possible to reduce the test time from five to three hours and thus differentiate the controls from the group of patients. No secondary side effects were observed with 5 g, which were present in 30% (6 cases) of the patients with doses of 25 g. In view of the results the use of 5 g in the test is indicated in the 3 hour test. Under these conditions 95% (1, 645 D.P.) for the controls excreted less than 1, 030 g (21%) of the doses administered.