In 11 juvenile diabetics and 13 control subjects, the secretin-pancreozymin test was performed. Duodenal-volume losses were corrected by use of radioactive vitamin B12 as marker substance. As compared to normal subjects, juvenile diabetics had significantly decreased pancreatic outputs of amylase, trypsin, chymotrypsin, and to a lesser degree, of bicarbonate. Clinical evidence of disease of the exocrine pancreas was missing. There was no discernible relationship between the abnormality of external pancreatic function and the duration of diabetes mellitus or the dose of insulin required. Possible factors that may be responsible for the exocrine deficiency of the pancreas in juvenile diabetics are discussed.