Using radioimmunoassay, we tested serum elastase 1 (E1), an enzyme secreted only from the pancreas, in 200 subjects as follows: 39 healthy subjects as controls, 56 patients with diseases of the digestive tract, 66 patients with hepatobiliary diseases, and 39 patients with pancreatic diseases. The serum E1 showed high specificity and proved very useful in the diagnosis of acute pancreatitis. However it was not useful in diagnosis of clinically silent chronic pancreatitis, nor in its functional evaluation. On the other hand, it was found to be a valuable guide in revealing a concomitant pancreatic pathology during hepatobiliary diseases. Further investigation is needed of the behavior of E1 in patients who have undergone a total pancreatectomy, where the enzyme remains measurable, and in those with an ileocolic disease in an acute phase where E1 is increased in many patients.