The distribution of U, Y, P, and Ca was studied with an electron microprobe in detrital zircons from paragneisses of amphibolite to granulite facies as well as in zircons formed in their present-day host rocks, such as a granite, anatectic and aplitic gneisses and a migmatite from the Southern Alps. Detrital paragneiss zircons have low trace element contents, whereas zircons formed in their present-day host rocks have elevated trace element contents. According to the isotopic U-Pb age pattern one may distinguish two types of zircon populations formed in their present-day host rocks: one which lost lead without any known exogene cause, and one the U-Pb system of which was only opened in response to a geological event. Different modes of incorporation of the trace elements in the zircon crystals are thought to be responsible for this different behaviour and are discussed.