Oral administration of 72 mg nitroethane/kg body weight d^-1 to ewes reduced (P<0.05) the specific activity of ruminal methane production (SARMP) by 26, 69 and 29% on days 1, 2 and 5 of treatment, respectively. Administration of 24 mg nitroethane/kg body weight d^-1 reduced (P<0.05) SARMP by 26 and 42% on days 1 and 2 but not on day 5 (13% reduction) of treatment. Rumen VFA production was unaffected by nitroethane administration. These results demonstrate that nitroethane reduces ruminal methanogenesis in vivo without redirecting the flow of reductant generated during fermentation to propionate and butyrate.