Rye straw was pretreated with ionic liquid and subjected to enzymatic hydrolysis to produce reducing sugars. The experiment had a Box-Behnken design. The aim of the optimization process was to maximize the yield of reducing sugars after enzymatic hydrolysis of rye straw and to determine the optimal conditions for biomass purification with ionic liquid and for enzymatic hydrolysis. The input variables for rye straw pretreatment were temperature, time and quantity of ionic liquid, and the input variables for enzymatic hydrolysis were time, temperature and the quantity of T. reesei and A. niger enzymes. The yield of reducing sugars was highest when rye straw was pretreated under the following conditions: time - 2 h, temperature - 120 degrees C, quantity of ionic fluid - 10 ml/10g DM rye straw, and subjected to enzymatic hydrolysis under the following conditions: time - 72 h, temperature - 50 degrees C, quantity of cellulase from T. reesei - 350 mu l, quantity of cellobiohydrolase from A. niger - 150 mu l. Model validation did not reveal significant differences between the approximated and measured values. (C) 2016 Elsevier Ltd. All rights reserved.