Pure pancreatic juice was obtained from within the pancreatic duct in 54 patients after endoscopic cannulation of the papilla of Vater. In all 20 normal subjects there was a brisk response to intravenous injections of GIH secretin in small dosage (1 and 4 CU). Peak bicarbonate concentrations occurred after a 4 CU stimulus, whereas volumes, and bicarbonate and protein outputs were greatest after 70 CU. Total protein and amylase concentrations were highest in the first specimens collected from each patient, and fell rapidly after stimulation. Plateau levels for all indices were achieved 10-20 minutes after starting infusions of secretin and pancreozymin. When normal patients and those with chronic pancreatitis were compared, there was considerable overlap in all indices (volume, bicarbonate and total protein concentrations) after bolus injections of secretin. Most patients with chronic pancreatitis achieved a peak bicarbonate concentration in excess of 100 mmol/l. The median concentrations were not significantly different from normal after any dose of secretin when pooled 10 minute samples were analysed. However there were significant differences in peak bicarbonate concentrations (after 1 and 4 CU, but not after 70 CU), when one minute samples were compared. There were also statistically significant differences in the median 10 minute responses for volume after 1 and 70 CU, for bicarbonate output after 1, 4, and 70 CU, and for protein output after 70 CU. The results of juice studies in patients believed to have early chronic pancreatitis did not differ significantly from those in normal subjects or those with chronic pancreatitis. Endoscopic duct cannulation cannot guarantee complete recovery of pancreatic secretions, and measurements of volume and output may be inaccurate. When standard biochemical indices are used, the diagnostic role of pure juice studies is limited; further research may reveal more specific disease markers.