After indirect stimulation of the pancreas by means of a test meal the intestinal activities of trypsin were determined in 452 subjects, lipase in 117, and phospholipase in 57. Trypsin levels were subnormal in 88%, lipase levels in 80%, and phospholipase levels in 81% of patients with chronic pancreatic disease. The outcome of repeated tests (trypsin) was completely consistent in 20 out of 22 patients. Calculations of ratios between the enzymes studied suggested that lipase was the enzyme most susceptible to pancreatic damage. Also in cases of celiac disease and after Polya gastric resection, the decrease of the intestinal lipase concentrations was more marked than that of the other enzymes. In 9% of the cases of chronic pancreatic insufficiency the diagnosis would have been overlooked if either lipase or trypsin had been determined as the sole enzyme. In clinical practice it is recommended to estimate at least two enzymes, because abnormal ratios may be of diagnostic value and because the two different groups of enzymes provide a mutual check on the secretory capacity of pancreatic enzymes. On the whole, the test was found to be reliable, simple, physiological, and inexpensive in terms of resources, and it is highly recommended as a routine test of the pancreatic function.