Extremophilic microorganisms are adapted to survive in ecological niches such as at high temperatures, extremes of pH, high salt concentrations and high pressure. These microorganisms produce unique biocatalysts that function under extreme conditions comparable to those prevailing in various industrial processes. Some of the enzymes from extremophiles have already been purified and their genes successfully cloned in mesophilic hosts. In this review we will briefly discuss the biotechnological significance of extreme thermophilic (optimal growth 70-80 degrees C) and hyperthermophilic (optimal growth 85-100 degrees C) archaea and bacteria. In particular, we will focus on selected extracellular-polymer-degrading enzymes, such as amylases, pullulanases, cyclodextrin glycosyltransferases, cellulases, xylanases, chitinases, proteinases and other enzymes such as esterases, glucose isomerases, alcohol dehydrogenases and DNA-modifying enzymes with potential use in food, chemical and pharmaceutical industries and in environmental biotechnology.