Soil obtained from a beech forest formed significant amounts of acetate when incubated in a bicarbonate-buffered, mineral salt solution under anaerobic conditions at both 5 and 20 degrees C (21 and 38 g of acetate per kg [dry weight] of soil, respectively). At 20 degrees C, following an 18-day lag period, rates of 0.07 mmol of acetate synthesized per g (dry weight) of soil per day were observed. Acetate was not subject to immediate turnover; methane and hydrogen were not formed during the time intervals (5 degrees C, 335 days; 20 degrees C, 95 days) evaluated. The synthesis of acetate from endogenous materials was coincident with acetogenic potentials, i.e., the capacity to catalyze the H(2)-dependent synthesis of acetate. Hydrogen consumption was not directed towards the synthesis of methane. Collectively, these results suggest that acetogenesis may be an underlying microbial activity of this forest soil.