The origins and clinical significance of hyperamylasemia during diabetic ketoacidosis are unclear. We have therefore correlated important clinical and laboratory indices of diabetic ketoacidosis with sequential determinations of serum and urine amylase concentrations, amylase/creatinine clearance ratios, and specific amylase isozyme types. Hyperamylasemia occurred in 79% of our patients with diabetic ketoacidosis, often after admission to the hospital. Among these patients, 48% had pancreatic-type, 36% salivary-type, and 16% mixed-type (pancreatic and salivary) hyperamylasemia. There were no correlations between the presence, degree, or isozyme type of hyperamylasemia and most laboratory or clinical characteristics, including gastrointestinal symptoms. Patients with pancreatic-type hyperamylasemia tended to have higher amylase/creatinine clearance ratios, but it was not possible to unequivocably diagnose acute pancreatitis during diabetic ketoacidosis with current routine clinical or laboratory procedures.