A novel methane-producing archaeon, designated strain HASU(T), was isolated from a lotus field. Cells were Gram-negative, non-motile, irregular cocci, 2-3 mum in diameter, and occurred singly. Growth was observed at 15-40 degrees C (optimum, 37 degrees C) and pH 6.5-7.5 (optimum, pH 7.0). The G+C content of the genomic DNA was 60.9 mol%. Strain HASU(T) utilized ethanol, 1-propanol, 1-butanol, hydrogen and formate for growth and methane production. It converted ethanol to methane and acetate. Based on comparative 16S rRNA gene sequence analysis, strain HASU(T) was shown to be affiliated with the genus Methanofollis. It was related most closely to the type strain of Methanofollis liminatans (96.1 % 16S rRNA gene sequence similarity). Based on phylogenetic analysis and phenotypic characteristics, strain HASU(T) is considered to represent a novel species of the genus Methanofollis, for which the name Methanofollis ethanolicus sp. nov. is proposed. The type strain is HASU(T) (=NBRC 104120(T)=JCM 15103(T)=DSM 21041(T)).