Isolation from beer of a sucrose-fermenting species of Zymomonas confirmed as Z. mobilis, is recorded.Motility and H2S production were variable and sensitive to precise environmental conditions. The beer-spoilage potential of this species was established as limited.A strain of Z. anaerobia was isolated which acquired sucrose-fermenting ability after growth in fructose.It is doubtful, therefore, whether the creation of two distinct species within this genus is valid.