The amylase/creatinine clearance ratio (Cam/Ccr ratio) was determined in 239 subjects. In 87 hospitalised patients without pancreatic disease (controls) the Cam/Ccr ratio was 3.02 +/- 0.69 (mean +/- ISD). The ratio was above the normal range in all patients with acute pancreatitis but was normal in those with chronic pancreatitis and carcinoma of the pancreas. In 18 patients with choledocholithiasis a raised ratio distinguished those with pancreatitis as assessed independently by the surgeon at laparotomy from those with a macroscopically normal pancreas. Raised Cam/Ccr ratios were also found in diabetics with ketoacidosis and in three patients with fulminant alcoholic liver disease. Though a positive correlation was found between the Cam/Ccr ratio and serum creatinine concentration, abnormally high ratios did not occur in 30 patients with chronic renal failure. A significant increase in Cam/Ccr ratios was produced in six healthy volunteers by intravenous injection of glucagon. However, it is unlikely that hyperglucagonaemia alone accounts for the increased Cam/Ccr ratio seen in acute pancreatitis, as no correlation was found between the clearance ratio and the plasma glucagon concentration in a series of patients. In two other patients in whom excess circulating pancreatic polypeptide was detected the Cam/Ccr ratio was normal. It is concluded that, in view of the sensitivity and relative specificity of finding an increased Cam/Ccr ratio in acute pancreatitis, its determination should be valuable clinically, especially in those cases of hyperamylasaemia where the cause is in doubt. The mechanism whereby the ratio is increased is unknown, and it is unlikely that either glucagon or pancreatic polypeptide is a major factor in its production.