Levansucrase from Bacillus subtilis C4 was applied to the production of levans from sucrose, using various temperatures and sucrose concentrations. These experiments, performed in high sucrose concentration solutions, demonstrated the ability of levansucrase to transform almost all the substrate available in the reaction medium. Analysis of the reaction products showed the enzyme catalysed the formation of both levan and fructo-oligosaccharides with a degree of polymerisation smaller than 50. Fructo-oligosaccharides were analysed using gel permeation and anion exchange HPLC. The chain length decreased while temperature and sucrose concentration in the reaction medium increased. Levans and fructo-oligosaccharides were formed simultaneously. Comparison of our product profiles with ion exchange HPLC chromatograms of inulin and of a solution of fructo-oligosaccharides produced by Aspergillus niger fructosyl-transferase showed that 1-kestose was probably the main oligosaccharide in the reaction medium, and that a great variety of other fructo-oligosaccharides were also produced, suggesting very poor specificity of levansucrase for the linkages it forms from sucrose.