Clinical features of CD may overlay the presentation of other diseases responsible for small intestinal anatomical and/or functional changes. Among these, FH is an important cause of chronic diarrhea in children with identical age-range of common CD presentation. The aim of this study was to evaluate the AAG-IgA and D-xylose absorption tests for differential diagnosis of CD and FH. We studied 10 patients, mean age 2.7 ± 1.6 years with CD (jejunal biopsy: total villous atrophy with hyperplasia of the crypts) and 14 patients, mean age 2.1 ± 0.9 years, with FH(jejunal biopsy: mild/moderate villous atrophy). IgA deficiency was ruled out. Serum AAG-IgA was measured by enzyme immunoassay (ELISA) (Gluten-IgA EIA, Pharmacia Diagnostics AB), abnormal levels: >30.3, expressed in Arbitrary Units, AU. D-xylose absorption test was performed using 0.5g/Kg followed by a 1 h and 2 h blood level determinations, normal values: >=30 mg/%. AAG-IgA values were higher in DC(240.4±136.2 AU) than in FH (19.3±8.5 AU) (p<0.001, Mann-Whitney test). On the contrary, D-xylose values were lower in CD(13.2±8.0 mg/%) than in FH (41.3±11.8 MG/%) (p<0.001). The combined use of both tests, AAG-IgA determination and D-xylose absorption test, showed sensitivity of 100% and specificity of 86% in diagnosis CD. Jejunasl biospsy was performed only in 2 out of 14 children with FH because AAG-IgA or D-xylose test was found abnormal. We concluded: 1) The determination of serum AAG-IgA and D-xylose absorption test are important methods for differencial diagnosis in patients with chronic diarrhea; 2) The combined use of the above two tests is reliable for screening patients for small intestinal biopsy.