A new test of intraluminal fat digestive activity is proposed for which a mixed triglyceride, 1,3-dioleyl-2-14C-decanoyl glycerol, was used. 29 normal subjects, 14 patients with proven chronic pancreatitis, 10 pancreatectomy, 12 villus atrophy and 8 bile acid-deficient patients were studied. The mean 14CO2 excretion in breath, expressed as the 10th-hour cumulative percentage of the administered dose, was 68.3% in the normal subjects, and only 32.9% in patients with pancreatic disease. There was almost no overlap between the normal subjects and the patients with proven organic disease. The test also allowed the detection of functional pancreatic insufficiency, due to impaired pancreatic stimulation in case of gluten enteropathy and severe malabsorption.