The possibility to produce lactic acid using mixed heterogeneous i.noculum found in cowdung has been demonstrated controlling physicochemical factors such as pH, temperature and the composition of the culture medium. At low pH values the principal final product was always ethanol while at higher pH values was always lactic acid, irrespective of the nitrogen source. Lactate production increased significantly when growth factors (.vitamins) were added to the culture media irrespective of the nitrogen source. The results indicate that mixed cultures could be grown on media with ammonium sulphate nitrogen source obtaining high yields of lactilc acid.