Sonocrystallization was used to speed-up the lactose recovery, from heat-induced deproteinated and concentrated 'paneer' whey (paneer resembles cottage cheese) having lactose content of 15.0-15.5% (w/v) (substantially low in comparison to conventional process that uses the whey with lactose concentration of 50-60%, w/w) and protein content of 0.4-0.53% (w/v), using ethanol as an anti-solvent (effective concentration of 85%, v/v). The lactose recovery by sonocrystallization was optimized for operating parameters like temperature, sonication time, initial pH, end pH, stirring and seeding at two distinct levels using L-12-orthogonal array method (MINITAB software). The mean responses were analyzed for lactose recovery and its purity. Seeding and initial and end pH of whey were observed to be the most influencing parameters for the lactose recovery and purity, respectively. The optimum levels for the process parameters have been identified. The lactose recovery of 90.3% in 20 min was observed at optimized levels. (C) 2007 Elsevier B.V. All rights reserved.