Although the aceticlastic methanoarchaea Methanosarcina and Methanosaeta employ different enzymes to catalyze the first step of aceticlastic methanogenesis, it has long been assumed that the remainder of the pathway was the same. Analysis of the recently completed genome sequence of Methanosaeta thermophila confirms that the majority of core steps of the pathway are similar in both genera, but striking differences have been discovered in electron transfer and energy conservation. In addition, the presence of genes encoding enzymes for the CO(2) reduction pathway in the Msa. thermophila genome suggests the possibility that Methanosaeta might be more metabolically diverse than previously thought. Thus, genome analysis of Msa. thermophila presents new research avenues for this forgotten methanogen and reminds us of the questions that still remain unanswered about aceticlastic methanogenesis in both Methanosaeta and Methanosarcina.