Exocrine pancreatic insufficiency (EPI) is an important cause of malassimilation in the dog. Due to the unreliability of available diagnostic procedures in the past the prevalence of EPI has probably been exaggerated. A new procedure has recently been developed and is proving to be highly sensitive and highly specific for the measurement of exocrine pancreatic function. This test, a radioimmunoassay of serum trypsin-like immunoreactivity, shows pronlise for more accurately distinguishing between EPI and small intestinal disease as the cause of malassimilation.