Many approaches have been proposed to differentiate between steatorrhea due to pancreatic insufficiency and intestinal disease. Bo-Linn and Fordtran recently suggested that fecal fat concentration (FFC) is a useful screening test for this distinction. Our aim was to validate their result in a large group of patients. Fecal fat concentrations were calculated for 613 fecal fat tests in 538 patients. Included were 88 patients with pancreatic steatorrhea (13 pancreatic carcinoma, 6 cystic fibrosis, and 69 chronic pancreatitis) and 525 with nonpancreatic steatorrhea. The mean FFC of patients with pancreatic disease (15.0 +/- 1.9 g%, mean +/- SEM) was significantly higher than that of patients with other diseases causing malabsorption (8.9 +/- 0.3 g%, p less than 0.001). Forty-two percent of patients with pancreatic steatorrhea had an FFC below 10 g%. The overlapping of the FFC of steatorrhea due to pancreatic disease and that produced by celiac disease, gastric resection, and other conditions suggests that this approach does not differentiate between pancreatic and intestinal steatorrhea.