The effect of three parameters (initial acetate concentration, temperature and pH) on the acetoclastic reaction was studied with the thermophilic methanogenic bacterium Methanosarcina sp. MSTA-1. The optimum temperature for growth ranged around 55 degrees C, and optimum pH was 6.5-7.5, giving a minimum generation time of 12.6-13.9 h (mu max = 0.050-0.055 h-1) and a maximum value of the specific acetate consumption rate (qmaxs) of 14-20 mmol/g cells per hour. Contrary to the methane yield, the growth yield was found to be dependent on culture conditions, especially on incubation temperature. Methanosarcina sp. MSTA-1 showed a low affinity for acetate substrate. Growth at 55 degrees C and at constant pH 7 resulted in a Km value and a threshold acetate concentration of 10.7 mM and 0.7 mM, respectively.