We determined the usefulness of pure pancreatic juice collected by endoscopic procedures for assaying impaired pancreatic function in patients with chronic pancreatitis. The functional findings were compared with the degree of morphological change in endoscopic retrograde pancreatograms. Samples of pancreatic juice were collected from 23 patients with suspected chronic pancreatitis by endoscopic cannulation after a bolus intravenous injection of secretin, 100 IU, for 20 min in four 5-min samples. Volume and amylase and bicarbonate concentrations were measured. The maximum bicarbonate concentration (MBC) was found in fractions collected after 10 min. The MBC in patients with chronic pancreatitis (n = 7) was lower than in normal subjects (n = 10) (p <0.05). When we regarded 125 mEq/L (mean - 1.5 SD) as the normal limit of MBC, the sensitivity, specificity, and overall efficiency of the pancreatic functional test using pancreatic juice to detect chronic pancreatitis were 86, 100, and 94%, respectively. In comparison with the group with normal pancreatogram findings (n = lo), the MBC, volume, amylase output, and bicarbonate output were lower in the combined group (n = 9) of Cambridge II and III (p <0.05). MBC was the most reliable parameter in the evaluation of the exocrine pancreatic functional test using pancreatic juice samples.