Methods and enzymic processing conditions for manufacturing low-lactose milk containing oligosaccharides were evaluated. Comparisons were made between the method of using beta-galactosidase to transform the lactose in milk into oligosaccharides directly and the method of applying ultrafiltration techniques to separate lactose from milk proteins and then transform the lactose in the permeate into oligosaccharides. Since the beta-galactosidase exhibited higher transgalactosylative activity in the permeate than in the milk and the higher the initial lactose concentration the higher the conversion to oligosaccharides, a useful procedure for manufacturing low-lactose high-oligosaccharides milk would be to separate milk proteins from lactose by ultrafiltration first, concentrate the UF permeate by evaporation, apply enzymic reaction in the concentrated permeate, and add the hydrolysate to the retentate to obtain the final milk product. The optimal conditions for the enzymic reaction in the permeate was 25.3% of initial lactose concentration, an EIS ratio of 6.7%, and carried out at 50 degreesC for 3.5 h. (C) 2002 Elsevier Science Ltd. All rights reserved.