The production of pullulanase and alpha-amylase by Clostridium thermosulfurogenes SV9 was optimized employing suitable environmental conditions and various nitrogen and carbon sources. The optimal temperature and pH values for the formation of pullulanase and alpha-amylase were 60 degrees C and 7.0, respectively. Maximum amounts of pullulanase and alpha-amylase were produced at the end of the exponential growth phase (12 h). Peptone with yeast extract (PYE) served as the best nitrogen source for the production of both enzymes. An increased amount of pullulanase (0.64 U/ml) and alpha-amylase (0.40 U/ml) were produced in PYE medium in the presence of mineral and vitamin solutions. The maximum amount of pullulanase was produced when potato starch served as substrate and wheat starch was the best substrate for alpha-amylase production.