Previous reports on the use of the serum amylase level to assess pancreatic injury in patients with blunt abdominal trauma have been disappointing. The availability of methods to measure the serum isoamylases (P & NP) might be expected to improve the accuracy with which the serum amylase level is used.Sixty-one patients treated for a variety of blunt trauma injuries were studied. All categories of injury were included. Isoamylase levels were determined from admission sera and were compared to injuries found at laparotomy. Three patients had major pancreatic injury but only two of these patients showed a rise in the pancreatic isoamylase. Sixteen additional patients had a rise in the pancreatic isoamylase without evidence of pancreatic injury. Eight of these patients had no component of abdominal injury whatsoever. Two patients with isolated head injury had substantial elevations of pancreatic isoamylase.The regulation of serum amylase is multifactorial and variable. The measurement of serum isoamylase levels does not offer great improvement over the serum amylase in evaluating patients with blunt abdominal trauma.