Twenty-one Saccharomyces strains isolated from a cider process were analysed in terms of karyotypes, Y' S. cerevisiae sequence occurrence, rDNA structure and cross-fertility with species tester strains. A strong predominance of S. bayanus var. uvarum G. Naumov was found (18 strains vs. three S. cerevisiae). Among the S. bayanus var. uvarum, only three strains proved to contain species-specific Y' S. cerevisiae sequences.