In order to evaluate the efficacy of a monoclonal pancreatic (P) isoamylase assay in the diagnosis of chronic pancreatic disease and to compare the behavior of this test with that of amylase and elastase 1, these three enzymes were measured in the sera of 39 healthy controls, 28 patients with pancreatic cancer, 50 with chronic pancreatitis and 60 with extra-pancreatic diseases. In patients with chronic relapsing pancreatitis, increased P-isoamylase and elastase 1 values were found in similar percentages (about 70%), whereas the percentage for elevated amylase values was lower (52%). Elastase 1 was increased in 52% of patients with pancreatic cancer, while the other two enzymes were only occasionally elevated. The levels for all three enzymes were abnormal in some patients with extra-pancreatic diseases. It may be concluded that this assay for P-isoamylase determination is sufficiently sensitive and reliable in detecting pancreatic inflammation, even though some limitations concerning its specificity should be born in mind.