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Several natural associations composed of thermophilic anaerobic bacteria capable of utilizing various cellulose materials at 60 ± 2°C and pH 6.0–7.0 were isolated from the sludge of Kamchatka geothermal springs. The rate of ethanol production (up to 1.7 g\l per day) and the concentration of ethanol in the medium (up to 1.2%), as well as the fermentation period (10–15 days), were determined under anaerobic conditions in the presence of cellulose, coniferous sawdust, newsprint, or paper pulp as a carbon source. Microorganisms were found that inhibited the production of ethanol. The initial pH value was found to influence both the ethanol production rate and ethanol\acetate ratio. A pH decrease from 7.0 to 5.0 led to a 6.7-fold increase in ethanol production and caused a 23.8-fold increase in the ethanol\acetate ratio.