Abstract: A novel group of radiolabelled diamines are provided, effective for pancreatic imaging and represented by the formula ##STR1## wherein n is 1 to 10; R.sub.1 and R.sub.2 are the same or different and are hydrogen, hydroxyl or lower alkyl having 1 to 6 carbon atoms; R.sub.3 is lower alkyl having 1 to 6 carbon atoms; and N' is a nitrogen atom forming part of a 4- to 8-membered heterocyclic ring containing one or two hetero atoms, one of which is said nitrogen, said heterocyclic ring being unsubstituted or substituted with one or more lower alkyl groups and pharmaceutically acceptable acid addition salts thereof.