Prokaryotic microfossils, found in early Archaean rocks, implies that the earliest life forms on Earth probably date from between 3.5 3.8 Ga ago, when living conditions on Mars were similar to those on early Earth. Therefore it is legitimate to assume that life on Mars emerged as well as on Earth. Accepting that first life on both planets was determined by complex microbial communities, the Martian life must have adapted to drastically changing environmental conditions or become again extinct. One possibility for survival of Martian primitive life might be subsurface lithoautotrophic ecosystems. Comparable environments exist in permafrost regions on Earth.The current ESA (European Space Agency) mission Mars Express determined existence of water as ground ice on Mars, which is fundamental requirement for life. Furthermore, Mars Express demonstrated for the first time the presence of CH4 in the Martian atmosphere, which due to the lifetime of CH4 could be only originated from active volcanism or biological sources. This finding may have important implications for the possibility that microbial life could exist on Mars.Methanogenic archaea colonising terrestrial permafrost, are highly specialized organisms from the view point of metabolism. The capability of these organisms to lithoautotrophic growth under strictly anaerobic conditions, tolerance to low temperatures and survival under extreme conditions of permafrost for several millions of years make methanogens one of the most suitable keystone organism for the investigation of possible Martian life.Within the scope of a project in the DFG (German Research Foundation) Priority Program Mars and the Terrestrial Planets we study the tolerances of methanogens under unfavourable life conditions of terrestrial or extraterrestrial permafrost (Mars simulation). The borders of growth influenced by desiccation, temperature extremes, radiation and high salt concentration were analyzed for the organisms in pure cultures obtained from permafrost soils as well as in their natural environment of Siberian permafrost.First results represent high survival potential of methanogenic archaea under tested extreme conditions. Methanogens revealed CH4 production under in situ temperature conditions (0 to 2°C) and salt concentration up to 6 mol with a rate of about 0.077 0.009 nmol CH4 h-1 g 1. Incubation of pure cultures with different salt concentration (0.1 to 6 mol) showed a significant CH4 production rate as well even at salt concentration of 6 mol (0.013 0.022 nmol CH4 h-1). Additionally, the influence of temperature on the salt tolerance of methanogens was analyzed. The organisms showed better adaptation to high salt concentration at temperatures of 4°C, with a CH4 production of 0.019-0.026 nmol CH4 h-1 compared to the activity at 28°C (0.012-0.014 nmol CH4 h-1).The comparative system studies will serve to understand the modern Mars cryosphere and other extraterrestrial permafrost habitats. This knowledge represents an essential basis for searching and understanding of extraterrestrial life, if present, especially concerning possible protected niches on present Mars.