The release of glucose-6-phosphate dehydrogenase (G6PD) from Candida guilliermondii, grown on rice straw hydrolysate, by vortex agitation with glass beads was studied. The effects of cell suspension concentration and disruption time on volumetric activity, total protein and specific activity were evaluated from a 2 2 full-factorial central composite design. By using the response surface methodology, a second-order model was proposed to represent enzyme specific activity as a function of disruption time (XI) and cell suspension concentration (X-2). Under optimum conditions (X-1 = 5 min and X-2 = 11.5 gl(-1) the model predicted a G6PD specific activity of 0.88 U mg(-1). (c) 2005 Elsevier Inc. All rights reserved.