The invention relates to substituted imidazopyridazinediones of general formula ##STR00001## wherein R.sup.1 and R.sup.4 are defined as in claim 1, the tautomers, the enantiomers, the diastereomers, the mixtures thereof and the salts thereof, which have valuable pharmacological properties, particularly an inhibiting effect on the activity of the enzyme dipeptidylpeptidase-IV (DPP-IV).