SummaryLactase (β-galactosidase) was found in the midguts of normal adult worker honeybees and in those fed with lactose. Sephadex G-200 chromatograms of midguts of both groups showed two enzyme activity peaks, molecular weights of lactase being determined as 238 000 and 40 000, respectively. The midgut lactase activity was increased significantly by feeding the bees with lactose.