Bacterial strains. Bacillus subtilis I 68 try-2, (designated 'I 68' in the text) was from the collection of this laboratory while BS 5 and MC~, kindly provided by Dr Dedonder, were mutants obtained from the 168 strain carried in his laboratory. These three strains were, respectively, low level inducible, high level inducible, and constitutive with regard to levan-sucrase production (personal communication from Dr Dedonder). They behave identically with respect to the newly detected sucrose hydrolyzing activity reported in this note. Growth conditions and experimental techniques. Cultures were grown in either basic salts composition A (Dedonder, 1960) or B (Anagnostopoulos & Spizizen, 1961), containing 0.5 % carbon source, 20 ,ug./ml. L-tryptophan and 0.05 % casein hydro- lysate. Inducers were added to exponential growth-phase cultures and samples removed at intervals into iced tubes containing chloramphenicol sufficient to give a final concentration of 25-50 ,ug./ml. and EDTA, when used, at a final concentration of 0~01-0~015 M. Suspensions were broken before assay either by lysozyme treatment or by sonic oscillation. Where necessary to eliminate compounds reacting in the assay, dialysis was carried out before determination of sucrose hydrolysis or levan synthesis activity.