In order to study whether or not mucosubstance increases occur in the pancreatic juice of patients with chronic pancreatitis, hexosamine was measured in duodenal aspirates during the secretin phase (S-40) following pancreozymin-secretin stimulation in 16 normal subjects, 37 patients with chronic pancreatitis, 6 patients with alcoholism, 13 patients with gallstones, and 11 patients with peptic ulcer. The hexosamine concentrations in the pancreatic secretions showed a negative correlation with the bicarbonate concentrations and volume output. Rises in hexosamine concentration were seen in alcoholism and chronic pancreatitis, especially in alcoholic pancreatitis. This is probably intimately related with the repeated ingestion of large amounts of alcohol over long periods of time. Since high hexosamine values are noted in the relapsing type of chronic alcoholic pancreatitis, increases in viscosity due to mucosubstance increases in the pancreatic juice are probably related with the recurrence of acute attacks accompanying ductal stenosis or obstruction.