Galactooligosaccharides (GOS) are beneficial to human health and can be produced from lactose on the ground of beta-galactosidase transferase activity. The aim of this work was to obtain dried buttermilk with maximal concentration of GOS. The laboratory trials with enzyme (Maxilact LX 5000) concentrations 0.1%, 0.4%, 0.8%, 1.2%, 1.6% and 2% (v/v) were made at first. Pilot experiment was carried out on spray dryer Niro Atomizer with the mixture of evaporated buttermilk and 15% (v/v) of ultrafiltration permeate and the enzyme concentration of 0.1% was chosen. Saccharides were analysed by HPLC. Degree of lactose conversion achieved 58.5% and 71.0% after 80 min (start of drying) and 130 min (end of drying) respectively. The final product contains 70 g/kg of GOS. There is no significant residual enzyme activity in dried buttermilk. (c) 2005 Elsevier Ltd. All rights reserved.