A rapid and reliable method to assess the potential specific activity of methagenic sludge is presented. The method is based on the gas chromatographic analysis for methane in the headspace of closed vials. Gas is sampled with a pressure lock syringe, which allows quantification independent of the pressure prevailing in the vials. The influence of various parameters as substrates, pH, NaCl and NH4 Cl concentrations on the activity of methaogenic sludge was investigated with this method. Data on the methanogenic activities on different substrate are discussed in terms of different physiological groups present in the sludge.