A boy with failure to thrive and isolated pancreatic amylase deficiency is described. Immunoprecipitation confirmed only salivary isoamylase in duodenal fluid at ages 20 and 33 months. Because normal pancreatic amylase messenger RNA was detected by reverse-transcriptase polymerase chain reaction in the fluid, failure of the normal maturation of pancreatic amylase secretion may explain the deficiency.