β-galactosidase (β-gal) activity level of 43 leuconostoc strains obtained from various traditionally made french cheese was evaluated. β-gal activity was determined on the permeabilized bacteria using toluene by measuring the rate of hydrolysis of 0-nitrophenil-β-D-β- galactopyranoside (ONPG). High level of variability was observed among the tested strains. Ninety three per cent of Ln. mes. subsp. mesenteroides, 91% of Ln. mes. subsp. dextraniam, 67% of Ln. citreum, one out of four strains of Ln. mes. subsp. cremoris and both of the Ln. lactis strains tested were positive.