When a user cannot find a word, he may think of semantically related words that could be used into an automatic process to help him. This paper presents an evaluation of lexical resources and semantic networks for modelling mental associations. A corpus of associations has been constructed for its evaluation. It is composed of 20 low frequency target words each associated 5 times by 20 users. In the experiments we look for the target word in propositions made from the associated words thanks to 5 different resources. The results show that even if each resource has a usefull specificity, the global recall is low. An experiment to extract common semantic features of several associations showed that we cannot expect to see the target word below a rank of 20 propositions.