SYNOPSISPancreozymin‐secretin tests were performed on 10 children with cystic fibrosis of the pancreas, who did not show any clinical symptoms of exocrine pancreatic insufficiency. The results indicate that in this particular group of patients water and bicarbonate secretion from the pancreas is more severely affected by the disease than enzyme secretion. Thus these patients secrete a small amount of pancreatic juice with a very low bicarbonate content but an abnormally high concentration of enzymes.Based on these results, a hypothesis for the pathogenesis of cystic fibrosis is put forward using the concept that in most exocrine glands, 2 different types of secretion contribute to the final secretory product: a highly concentrated secretion of organic substances and a more dilute secretion containing mainly electrolytes. During the secretory process, the organic constituents of the first type of secretion are diluted by the electrolyte‐containing fluid of the second secretion. Evidence is presented, that the pathological features in the pancreas in cystic fibrosis could result from the failure to produce an adequate amount of electrolyte‐containing fluid and it is suggested that the changes occurring in other organs affected by the disease may result from a similar pheno