Galacto-oligosaccharides (GalOS) were continuously produced using lactose and immobilized beta-galactosidase from Bullera singularis ATCC 24193 in a packed bed reactor. Partially purified beta-galactosidase was immobilized in Chitopearl BCW 3510 bead (970 GU/g resin) by simple adsorption. 55% (w/w) oligosaccharides was obtained continuously with a productivity of 4.4 g/(litre-h) from 100 g/litre lactose solution during a 15-day operation. Batch productivity was 6.5 g GalOS/(litre-h) from 300 g/litre lactose. (C) 1998 Elsevier Science Ltd. All rights reserved.