A municipal biomass waste based on rye straw or cardboard was sep. subjected to hydrolysis (temp. 60 degrees C, time up to 8 hrs), by using a 2% aq. NH3 or H2O. The NH3 hydrolyzates (previously purified from NH3 by using a polypropylene membrane and H2SO4) as well as aq. hydrolyzates were used to assess the efficiency of biogas production. The efficiency of CH3 prodn. from NH3 hydrolyzates was 5 times higher than from aq. hydrolyzates.