Compounds of the formula Ia or IB ##STR00001## where A is a saturated or monounsaturated heterocyclic, 4 - to 8-membered ring which contains one or two nitrogen atoms, and their tautomeric forms, possible enantiomeric and diastereomeric forms, their prodrugs and possible physiologically tolerated salts are useful as inhibitors of the enzyme poly(ADP-ribose)polymerase.