The cosecretion of pancreatic lipase and colipase are important in normal fat digestion. As adsorption of phosphatidylcholine to the lipid substrate interferes with lipase activity, hydrolysis to lysophosphatidylcholine with subsequent desorption is also essential for fat digestion. There are some data regarding the secretion of pancreatic phospholipases in normal adults but none in children or patients with pancreatic disease. In the present study, we aimeda) to develop an accurate fast assay method to measure phospholipase A2andb) to determine the secretion rate of pancreatic phospholipase A2and whether it is cosecreted with lipase and colipase in children with exocrine pancreatic dysfunction. Nine male patients aged 0.5 to 16 y (seven with cystic fibrosis, two with malabsorption) underwent pancreatic stimulation tests. Their colipase and lipase secretion rates were measured by titrimetric methods and phospholipase A2and A1by phosphorus magnetic resonance spectroscopy (31P NMR). It was found that the phospholipases, colipase, and lipase were absent in the two patients with pancreatic insufficiency. In patients with normal absorption, there were marked inter-and intrasubject variations of lipase, colipase, and phospholipase secretion rates that were consistent with the degree of exocrine pancreatic dysfunction. However, in the three 20-min stimulation periods of the pancreatic function test, pancreatic phospholipase is cosecreted with lipase and colipase, and average colipase and phospholipase A2secretion rates follow a similar or parallel pattern. These findings are consistent with the important role of pancreatic phospholipases in intestinal phospholipid hydrolysis leading to the desorption of phospholipids from the lipid substrate and enhancing lipid hydrolysis and phospholipid absorption.