With flocculent cells of Zymomonas mobilis levan was produced in a continuous upflow-tower fermentation with a productivity of up to 16 gl-1h-1. A large-scale process basing on whole Zymomonas cells is thought to be economical, if levan and ethanol production can be carried out simultaneously. Levan sucrase as the enzyme responsible for levan biosynthesis was purified and partially characterized.