Exocrine pancreatic insufficiency (EPI), a disease marked by chronic diarrhea and weight loss, is most commonly seen in German Shepherd Dogs. This condition is almost exclusively caused by atrophy of pancreatic cells that secrete digestive enzymes. This disease process is termed pancreatic acinar atrophy (PAA). Previous research has indicated that PAA is inherited in the German Shepherd Dog population of Finland. While the development of a serum assay for the major pancreatic digestive enzyme, canine trypsin-like immunoreactivity (cTLI), has led to a more accurate diagnosis of this condition, serum cTLI concentrations in affected dogs are normal prior to the development of PAA. Therefore, it has not been possible to take measures to decrease the incidence of this disorder. This project was designed to establish a pedigree of German Shepherd Dogs with EPI caused by PAA, confirm the inheritance of PAA, identify a marker for PAA in the genetic code, and develop an assay for this genetic marker. Results from this research will allow the screening of German Shepherd Dogs intended for breeding for carrier status for this disease and may lead to the eradication of this disease in the German Shepherd Dog breed.