Medium optimisation for a novel halophilic eubacterium, strain SX15, resulted in a 20-fold increase of extracellular xylanase activity. This facilitates the purification of xylanase produced by this strain. Prior experiments revealed that xylan concentration, source and concentration of nitrogen and salinity were important variables for xylanase production. Based on this, we adopted a fractional factorial design to determine the best combinations and approximate levels of these values. Subsequently, response surface (RS) methodology was applied to locate the optimal levels of xylan, NH4Cl and salinity. (C) 2003 Elsevier Science Inc. All rights reserved.