Semantically tagged corpora are becoming an urgent need for training and evaluation within many applications. They are also the natural accompaniment of semantic lexicons, for which they constitute both a useful testbed to evaluate their adequacy and a repository of corpus examples for the attested senses. It is essential that sound criteria are defined for their construction and a specific methodology is set up for the treatment of various semantic phenomena. We present some observations and results concerning the lexical-semantic tagging of an Italian corpus within the framework of two projects: the ELSNET feasibility study, part of a preparatory phase started with Senseval/Romanseval, and an Italian National Project (TAL), where one of the components is the lexical-semantic annotation of larger quantities of texts for an Italian syntactic-semantic Treebank. The results of the ELSNET experiment have been of utmost importance for the definition of the technical guidelines for the lexical-semantic level of annotation of the Treebank.