Enzymes from extremophiles operate at conditions that are different from their 'normal' counterparts, and are therefore a useful extension of the enzyme toolbox. In this paper, the direct glucosylation reaction mediated by a hyperthermophilic beta -glucosidase from Pyrocuccus furiosus was investigated. Hexanol was successfully coupled to glucose with this enzyme. A preliminary study was conducted to improve the product yield. A maximum product concentration of 12.9 g.l(-1) was attainable by increasing the glucose concentration to the maximum solubility of 2000 g.(kg buffer solution)(-1) at the reaction temperature. The highest glucose based yield of 2.64% was achieved with a glucose concentration of 900 g.(kg buffer solution)(-1) at a reaction temperature of 65 degreesC and a pH of 6.0. Performing the reaction at higher pH and temperature led to lower product concentrations. This was caused by deactivation of the enzyme accompanied by browning of the reaction mixture. A pH of 4.4 did have a negative effect on both the storage and the operational stability of the enzyme.