The enzyme from Streptomyces specifically hydrolyses the terminal lacto-N-biosyl residue (beta-D-Gal-(1->3)-D-GlcNAc) from the non-reducing end of oligosaccharides with the structure beta-D-Gal-(1->3)-beta-D-GlcNAc-(1->3)-beta-D-Gal-(1->R). Lacto-N-hexaose (beta-D-Gal-(1->3)-beta-D-GlcNAc-(1->3)-beta-D-Gal-(1->3)-beta-D-GlcNAc-(1->3)-beta-D-Gal-(1->4)-D-Glc) is hydrolysed to form first lacto-N-tetraose plus lacto-N-biose, with the subsequent formation of lactose. Oligosaccharides in which the non-reducing terminal Gal or the penultimate GlcNAc are replaced by fucose or sialic acid are not substrates. Asialo GM1 tetraose (beta-D-Gal-(1->3)-beta-D-GalNAc-(1->3)-beta-D-Gal-(1->4)-D-Glc) is hydrolysed very slowly, but lacto-N-neotetraose (beta-D-Gal-(1->4)-beta-D-GalNAc-(1->3)-beta-D-Gal-(1->4)-D-Glc) is not a substrate