Zygosaccharomyces Marxianus andSaccharomyces macedoniensis belong to the same species. This species is met with in the haplophase (Z. Marxianus) as well as in the diplophase (S. macedoniensis). It was possible to bring this yeast from the haplophase into the diplophase and vice versa. By keeping this yeast during long times on maltagar it showed a tendency to change from the haplophase into the diplophase, but not into the opposite direction. It seems quite possible thatHansen, who did not describe a conjugation in this yeast, had met with the diplophase. It has been once more emphasized — at whichWinge andLaustsen and alsoLindegren andLindegren have pointed —, that the genusZygosaccharomyces is no valid genus. The yeast studied here belongs to the genusSaccharomyces and must be designated with the original name given to it byHansen:Saccharomyces Marxianus. For the sake of completeness it is mentioned here that also an imperfect stage ofS. Marxianus has been describedviz., Candida macedoniensis (A. Castellani) Berkhout (I).Saccharomyces fragrans Beijerinck has to be considered as its synonym.