AbstractSpecies of the generaSaccharomyces,Schizosaccharomyces,DebaryomycesandSchwanniomyceswere compared from their extent of divergence in three regions from small (18S) and large (25S) subunit ribosomal RNAs comprising a total of 900 nucleotides. With the exception of the closely relatedSaccharomyces bayanusandS. pastorianus, which appear to have identical sequences, all other species could be distinguished by nucleotide differences in a variable region of the large subunit, and genus‐specific nucleotides were discernible in all three regions. The taxonD. tamariidiffered markedly from other species and is excluded fromDebaryomyces. By contrast,Schwanniomyces occidentalisshowed few nucleotide differences withDebaryomycesspp. and its transfer toDebaryomycesis proposed.Schizosaccharomycesproved to be somewhat more divergent thanSaccharomycesandDebaryomyces, but species differences appear insufficient for dividing the genus. Some of the factors influencing estimates of phylogenetic distances from rRNA sequences are discusse