By means of morphological criterions, two genetic groups of zircons could be recognized in the Freistadt Granodiorite Pluton, a felsic high-level I-type pluton in northern Austria: newly formed (N-type) zircons that nucleated in the granodiorite melt, and zircon xenocrysts (X-type zircons) that were incorporated by wall rock assimilation during magma emplacement. The N-types are small and have high elongation ratios and large (110) and (101) faces. These morphological properties refer to the physical and chemical conditions of the granodiorite melt and are exactly those which are to be expected in rapidly cooled felsic I-type granitoids. The xenocrysts are strikingly different and form two subgroups, which can be clearly correlated to the zircon populations of two distinctly older granitic wall rocks of the granodiorite pluton. The number of xenocrysts suggests that the granodiorite body contains on average ca. 10 %, locally at its margins up to ca. 20 % assimilated country rock material. This inherited material must have undergone a generally high degree of dissolution, for there are hardly any macroscopic indications of contamination in the granodiorite pluton. The zircon xenocrysts, however, show no signs of resorption and are euhedral, similarly to the N-types. The identification of zircon xenocrysts is therefore suggested to be one of the most potentially successful methods of recognizing and estimating the nature and extent of wall rock contamination in granitic intrusions.