A diagnostic agent for pancreatic exocrine function comprising a dipeptide represented by the following formula (I):X1—R1—Y1 (I)or a pharmaceutically acceptable salt thereof,wherein X1 is a protecting group,R1 is a phenylalanine, glutamine, valine, tyrosine, methionine, serine or threonine residue, andY1 is a 13C-labeled alanine molecule optionally having a protecting group.