Permafrost environments within the Siberian Arctic are natural sources of the climate-relevant trace gas methane. In order to improve our understanding of present and future carbon dynamics in high latitudes, we studied the activity and biomass of the methanogenic communities in terrestrial and submarine permafrost deposits. For these investigations, permafrost cores of Holocene and Late Pleistocene age were drilled in the Laptev Sea region. A high CH4 concentration was found in the upper 4 m of the Holocene deposits, which correlates well with the methanogenic activity and biomass. Even the incubation of core material at -3°C and -6°C showed a significant CH4 production (range: 0.040.78 nmol CH4 h-1 g-1). The results indicated that the methane in permafrost deposits originated from modern methanogenesis by cold-adapted methanogenic archaea. Microbial-generated methane in permafrost sediments is, so far, an underestimated factor for future climate development.