Abstract. This paper presents an indexing technique based on WordNet synonyms and holonyms. This technique has been developed for the Geographical Information Retrieval task. It may help in finding implicit geographic information contained in texts, particularly if the indication of the containing geographical entity is omitted. Our experiments were carried out with the Lucene search engine over the GeoCLEF 2006 set of topics. Results show that expansion can improve recall in some cases, although a specific ranking function is needed in order to obtain better results in terms of precision.