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Selection of suitable surfactants for enhancing and stabilizing α-amylase of Geobacillus thermoleovorans.Geobacillus thermoleovorans was cultivated in shake flasks containing 50 ml of starch-yeast extract-tryptone (SYT) medium with/without surfactants. Titres of the enzyme in media were monitored. The enzyme was also preserved at 4°C with/without surfactants and enzyme activities were determined. Among polyethylene glycol (PEGs) of different molecular weights, PEG 8000 (0·5%, w/v) caused a slight increase in the enzyme titre, while Tween-20, Tween-40 and Tween-60 (0·03%, w/v) exerted a significant stimulatory effect on enzyme secretion. In the presence of SDS, Tween-80 and cholic acid (0·03%, w/v), the enzyme production was nearly twofold higher than that in the control. The anionic (SDS, cholic acid) and non-ionic (Tweens) detergents increased the cell membrane permeability, and thus, enhanced α-amylase secretion. Furthermore, anionic surfactants exhibited stabilizing effect on the enzyme during preservation at 4°C.PEG 8000 and the ionic detergents (SDS, cholic acid and Tween-80) were more effective in the solubilization of cell membrane components, and enhancing enzyme yields than the cationic detergents such as CTAB (N,Cetyl-N,N,N-trimethyl ammonium bromide). Further, these surfactants were found to stabilize the enzyme at 4°C.The secretion of Ca2+-independent hyperthermostable α-amylase was enhanced in the presence of certain anionic and non-ionic detergents in the medium. Furthermore, the surfactants stabilized the enzyme during preservation at 4°C. The use of this enzyme in starch hydrolysis eliminates the addition of Ca2+ in starch liquefaction and its subsequent removal by ion exchange from sugar syrups.