The characteristics of levan formation by different preparations of levansucrase (free and immobilized enzyme and toluene-permeabilized whole cells), derived from recombinant levansucrase from Zymomonas mobilis expressed in Escherichia coli, were investigated. The maximal yield of levan by the three preparations were similar and were about 70-80% on a fructose-released basis with sucrose as nutrient at 100 g l(-1). Immobilized enzyme and toluene-permeabilized whole cells produced low molecular weight levan (2-3 x 10(6)), as determined by HPLC while high molecular weight levan (>6 x 10(6)) was the major product with the free levansucrase. The size of levan can thus be controlled by immobilized levansucrase and toluene-permeabilized whole cells in high yield.