Lactose (C12H22O11), also called milk sugar, is a disaccharide that consists of Beta-D-galactose and alpha/Beta-D-glucose through a Beta1-4 glycosidic linkage. Lactose is the major sugar and makes up 2-8% of milk. Simple, direct and high-throughput assays for lactose determination find wide applications. This assay uses specific enzyme-coupled reactions in which lactose is cleaved and the resulting galactose forms a colored product. The color intensity at 570nm or fluorescence intensity at 530nm/585nm is directly proportional to the lactose concentration in the sample.