We have studied the secretin-pancreozymin stimulation test of pancreatic function with particular regard to its usefulness in the diagnosis of cystic fibrosis patients without gastrointestinal symptoms. We have compared the test results in 38 control individuals, 14 patients with cystic fibrosis and five other patients with problems affecting pancreatic function. Of the cystic fibrosis patients tested, six had no gastrointestinal symptoms and were shown to have normal or raised output of pancreatic enzymes measured (lipase, trypsin, chymotrypsin, and amylase). There was a positive correlation between both volume and bicarbonate measurement versus body weight in all subjects, but this relationship was clearly different in the cystic fibrosis patients compared with others regardless of the cystic fibrosis patients' ability to secrete pancreatic enzymes. Among the cystic fibrosis patients, bicarbonate concentration tended to be higher in those able to secrete a significant amount of pancreatic enzymes. However, the actual output of bicarbonate measured in all cystic fibrosis patients (range 0.001-0.037 mmol/kg/45 min post-stimulation) was below that found in all control patients (range 0.104-0.516 mmol/kg/45 min post-stimulation). Therefore the secretin-pancreozymin test of pancreatic function appears to be useful in the diagnosis of cystic fibrosis even in those patients with adequate enzyme production.