In totally pancreatectomized patients breath 14CO2 excretion after ingestion of 14C-labeled triolein was significantly increased by a granulated pancreatic enzyme preparation and was reduced when pectin was added to the enzyme supplement. In the same patients pectin reduced trypsin, lipase, and amylase activities of jejunal aspirates after a test meal supplemented with pancreatic enzyme substitution, which was shown to give good enzyme activities in the intestine. In patients with chronic pancreatitis, breath 14CO2 excretion was reduced by wheat bran, which also caused a reduction in lipase and amylase activities of duodenal aspirates after a test meal. The findings demonstrate the efficiency of treatment with a granulated pancreatic enzyme preparation in restoring intraluminal enzyme activities and fat absorption in patients with pancreatic insufficiency. They also show that pectin and wheat bran may induce fat malabsorption and inhibit digestive enzyme activities in vivo.