The occurrence and expression of beta -galactosidase among various dextran-producing Leuconostoc strains was determined. beta -Galactosidase was detected from four of twelve Leuconostoc strains tested. beta -Galactosidase in L. mesenteroides was induced by lactose and was repressed by glucose. Growth curves of L. mesenteroides on lactose indicated extended lag and late growth phases that were shortened when the inoculum was preexposed to lactose.