[en] Methanothermus fervidus belongs to the group of hyperthermophilic Archaea. The Archaea comprise organisms that live under environmental extremes. like high temperature, low pH value or high salt concentration. The outer surface of the pseudomurein sacculi of the cells of Methanothermus fervidus is covered by glycoprotein subunits (S-Iayer) directly exposed to the extreme environment. The elucidation of the crystal structure of this surface glycoprotein may provide important information on the survival strategies of these unusual micro-organisms. Before our investigations neither three-dimensional crystals have been obtained nor X-ray analyses were performed. Only electron microscopic and computer image enhancement techniques have been applied to obtain structural information from crystalline two-dimensional S-layer sheets. We describe here the successful crystallization of this surface glycoprotein under microgravity conditions.