A cell extract of Thermococcus hydrothermalis, grown for 6 h, gave alpha-glucosidase activity at 14.9 U/l, degrading oligosaccharides and maltose. alpha-Amylase, alpha-glucosidase and pullulanase activities were detected at 289 U/l, 13.5 U/l and 30 U/l respectively in the culture medium after 24 h growth of the archaeum. All of three enzymes, characterised by a half-life of 1 to 5 h at 95 degrees C, degraded both the alpha(1-->4) and alpha(1-->6) linkages of polysaccharides and the alpha(1-->4) linkages of oligosaccharides.