Diamine oxidase (DAO) is an enzyme located almost exclusively in the villus tip enterocytes of mammals. Its plasma activity, normally very low, is enhanced by intravenous heparin that releases the enzyme from the enterocytes into the blood. Postheparin plasma DAO (PHD) values have been shown to be significantly reduced in patients with malabsorption and villus atrophy and in patients with Crohn's disease, thus suggesting that this test explores the mucosal integrity. The execution of the PHD test requires 8 blood samples over a period of 120 min after an intravenous injection of 15,000 IU of heparin, and then the calculation of the area under the curve. The aim of this study was to simplify the test and make it more acceptable by choosing only one of the eight curve points required for the calculation of the area under the curve and then assessing its discriminant power in different small bowel diseases. To this end, a discriminant analysis was performed on PHD curves of 16 normal subjects, 25 patients with celiac disease, 14 patients with treated celiac disease, 5 patients with diffuse primary small bowel lymphoma, 4 patients with small bowel lymphoma during treatment, and 55 patients with small bowel Crohn's disease. Plasma DAO values assayed 1 h (T60) after the injection of 15,000 IU of heparin proved to be the best discriminator curve point and the use of the T60 point alone may be usefully employed instead of the area under the 120-min curve.(ABSTRACT TRUNCATED AT 250 WORDS)