Culture variables affecting phytase production by a thermophilic mould Sporotrichum thermophile in submerged fermentation were optimized. Soluble starch, peptone, Tween-80 and sodium phytate were identified by Plackett-Burman design as the most significant factors to affect phytase production. The 2 4 full factorial central composite design of response surface methodology was applied for optimizing the concentrations of the significant variables and to delineate their interactions. Starch, Tween-80, peptone and sodium phytate at 0.4%, 1.0%, 0.3% and 0.3% supported maximum enzyme titres, respectively. An overall 3.73-fold improvement in phytase production was achieved due to optimization. When sodium phytate was substituted with wheat bran (3%), the phytase titre in the former was comparable with that in the latter. (c) 2007 Published by Elsevier Ltd.