The effect of self-administration (ad lib) of pancreatic enzyme substitution (Pancrease) in comparison with the dosage recommended by the manufacturer on abdominal symptoms and nutritional variables was studied in 10 patients with chronic pancreatitis. Both dosages were started in randomized order and they were continued for 4 weeks. Before and after each period of administration the patients were studied physically and weighed, and laboratory tests were performed. In addition, the patients kept daily records of pain (score, 0-3), bowel movements, amount of medication needed for maximum relief of symptoms and other remarks, if any. During self-administration, the number of capsules taken increased (5 +/- 1.3 to 11.4 +/- 2.4; p less than 0.001), the frequency of bowel movements decreased (3.6 +/- 1.4 to 1.6 +/- 0.7; p less than 0.05), and the pain was also relieved significantly (2.2 +/- 0.7 to 1.1 +/- 0.7; p less than 0.05) when compared with the regular dosage. Self-administration of the preparation did not have any significant effects on nutritional variables. Dryness of the mouth was the only complaint during self-administration of the drug in 4 of 10 patients. In conclusion, this study in selected patients with chronic pancreatitis indirectly supports the presence of a negative feedback regulation of exocrine pancreatic secretion in man. Thus, it may be beneficial to try self-administration of pancreatic enzyme substitution in selected patients to achieve maximum relief of symptoms in chronic pancreatitis.