Soil was used as seed without pretreatment for the fermentation of lactate in order to produce H-2. When the pH was kept at a constant level, H-2 production occurred in three steps. The first was the production of small amounts of H-2 during the initial growth of the microflora. Then, after a reasonably long period of inactivity during the cultivation stage, a large amount of H-2 was produced in additional two steps. It was found that the reduction of the pH after the initial growth phase had a positive effect on the H-2 yield. After cell growth at pH 6 and cultivation at pH 5, a total H-2 yield of 154 mmol l(-1) was achieved. It was found that acetate was essential for the rapid H-2 formation. On the other hand, even small initial concentrations of butyrate impeded the H-2 formation. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.