The potential for methane oxidation was measured, and methanotroph gene sequences studied, in a peat core from the Moorhouse Nature Reserve, UK. Methane oxidation potential was observed in all depths of the peat core (down to 30 cm), and was inhibited by addition of acetylene, indicating the involvement of methane-oxidising bacteria. A peak of activity was shown in the 10-12 cm horizon, below which activity decreased with depth. Above this horizon, methane oxidation was relatively high and showed little change with depth. 16S rDNA libraries from several sections of the peat core were screened with methanotroph 16S rDNA probes designed to detect the genera Methylomonas, Methylococcus, Methylobacter and Methylosinus. Two clones, MHP14 and MHP17, hybridised strongly with the Methylosinus probe and upon complete sequencing and phylogenetic analysis were shown to group closely to the Methylosinus/Methylocystis genera of methanotrophs. However, the clones do form a distinct branch of their own, supported by BOOTSTRAP values, and may represent a novel group of acidophilic methanotrophs which have yet to be cultured.