 From December 1971 onwards, Mittelberger was professor for Comparative (Indo-European) linguistics at the University of Graz, and from 1973-1988 also director of the Institute for translation studies ("Institut für Übersetzer- und Dolmetscherausbildung").His research centered on the proto-Indo-European language, the Indo-European languages of (old) Anatolia, Indo-Aryan languages (Sanskrit, Middle Indic), Iranian (Old Persian, Avestic, Middle Iranian), Greek (including Linear B), Latin and languages of old Italy, as well as Germanic with special interest in Gothic.Mittelberger was a very knowledgeable scholar and earlier known as a brilliant Indo-Europeanist.