Biogas production from lignocellulose-rich agricultural residues is gaining increasingly importance in sustainable energy production. Hydrolysis/acidogenesis (H/A) of lignocellulose as the initial rate-limiting step deserves particular optimization. A mixture of straw/hay was methanized applying two-phase digester systems with an initial H/A reactor and a one-stage system at different, meso- and thermophilic temperatures. H/A was intensified with increasing pH values and increasing temperature. H/A fermenters, however, were prone to switch to methanogenic systems at these conditions. Substrate turnover was accelerated in the bi-phasic process but did not reach the methanation efficiency of the single-stage digestion. There was no indication that two different cellulolytic inocula could establish in the given process.