Two out of three extremely thermophilic anaerobic archaea, isolated from deep-sea hydrothermal vents, produced pullulanase activity in the presence of maltose in the growth medium. Enzyme activities were mainly extracellular and characterized by optimum temperatures of 95 degrees C and 80-95 degrees C, optimum pH of 5.0-7.0 and a high degree of thermostability. One strain when grown in a fermenter with maltose as inducer produced pullulanase at 35 U/I.