Pancreatic replacement enzymes have been used for treatment of cystic fibrosis since shortly after the disease was first described in 1938. These enzymes were introduced into medical practice before the passage of the Food Drug and Cosmetics Act. The study proposed here is one of many which are now necessary to establish efficacy (to the standards of an FDA new drug application) of pancreatic enzymes for treatment of CF. Corresponding studies of these enzymes in non-CF patients (primarily adults with pancreatitis) are also being done in other centers. The specific aim of the study is to compare fat absorption (as determined by a 3-day stool fat determination) in CF patients during administration of pancreatic enzyme replacement with meals and during administration of a placebo preparation. The null hypothesis is that the administration of pancreatic digestive enzymes (CreonR-20) will have no beneficial effect on fat absorption in patients with cystic fibrosis. Twenty-three subjects were enrolled in this project. The study is closed and data analysis is in progress.