Wine yeasts were isolated from fermenting Garnatxa and Xarel.lo musts fermented in a newly built and operated winery between 1995 and 2000. The species of non-Saccharomyces yeasts and the Saccharomyces cerevisiae strains were identified by ribosomal DNA and mitochondrial DNA RFLP analysis respectively. Non-Saccharomyces yeasts, particularly Hanseniaspora uvarum and Candida stellata, dominated the first stages of fermentation. However Saccharomyces cerevisiae was present at the beginning of the fermentation and was the main yeast in the musts in one vintage (1999). In all the cases, S. cerevisiae took over the process in the middle and final stages of fermentation. The analysis of the S. cerevisiae strains showed that indigenous strains competed with commercial strains inoculated in other fermentation tanks of the cellar. The continuous use of commercial yeasts reduced the diversity and importance of the indigenous S. cerevisiae strains.