Most of the techniques used in Information Retrieval relyon the identification of terms from queries and documents, as much to carry out calculations based on the frequencies of these terms as to carry out to comparisons between documents and queries. Terms coming from the stem, either by morphological inflection or through derivation, can be persumed to have semantic proximity. The conflation of these words to a common form can produce improvements in retrieval . The stemming mechanism used depend directly on each language. In this paper, a stemmer for Spanish and the tests conducted by applying it to the CLEF Spanish document collection are described and, the results are discussed