The present invention relates to substituted imidazo[4,5-d]pyridazin-4-ones of general formula ##STR00001## wherein R.sup.1 to R.sup.3 and n are defined as in claims 1 to 8, the tautomers, enantiomers, diastereomers, 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).