Methanogenic organisms were isolated from sediments of Skan Bay, Alaska, and the Nankai Trough off the coast of Japan. The samples from Skan Bay (53°37'N-167°03'W) were from 32 to 39 cm below the sediment-water interface, under about 65 m of water. The temperature of these sediments remains below about 4°C year-round. The samples from the Nankai Trough were 247 m below the sediment-water interface, under about 900 m of water. The samples were taken from a zone containing methane hydrates, at an in situ temperature of about 15 to 18°C. We modified the Hungate techniques for growth of strict anaerobes to accommodate the very slow growth rates of the methanogens at low temperatures, and with these techniques we were able to enumerate and isolate methanogens, including aceticlastic methanogens, H₂-using methanogens, and methylotrophic methanogens. We also demonstrated the presence of syntrophic bacteria that required as much as a year to grow in culture, but we have not yet been able to obtain these organisms in pure cultures or co-cultures. The methanogens isolated from Skan Bay grew at temperatures near 4°C, but all were also able to grow at significantly higher temperatures. Analysis of ribosomal RNA of these methanogens indicates that they all belong within known genera of methanogens, although several of the isolates appear to represent new species.