The test of d-xylose concentration in blood has been used for approximately two decades for the examination of the absorption. The authors compared in 261 cases the total d-xylose blood level with the histological picture of the small intestine. Good correlation was observed between the 2 examinations. The d-xylose loading was found to select with favorable efficacy the new cases of celiac disease, of 63 fresh diagnosed subtotal and total villus atrophy cases the blood level of 61 was under the 1,64 mmol/l limit. At the 3rd stage of partial villus atrophy the blood level was pathological in 17 new patients. The sensitivity of the examination was 92.2% in selection of the new cases. Significant differences were found between the new cases and patients with excess gliadin (0.929 +/- 0.44 mmol/l and 1383 +/- 0.052 mmol/l) with identical rate of duodenal tissue impairments. On this basis the significant decrease of d-xylose level (0.5-1 mmol/l) must be regarded as the sign of relapse in patients with excess gliadin. Giardia lamblia and slight villus impairment was found in the biopsy material of further 28 children. The d-xylose level was pathological in 14 of them. D-xylose absorption was pathological before treatment in each of the 13 patients with contaminated (Gram-negative aerobic bacteria) small intestinal syndrome. D-xylose test is a useful method in the diagnostics of conditions associated with malabsorption and completed with other techniques it provides means for the separation of conditions associated with the diffuse impairment of the small intestine.