The filamentous non-heterocystous cyanobacterium Oscillatoria chalybea showed molecular hydrogen photoevolution under different conditions. The major part of determined hydrogen evolution would be derived from a hydrogenase system distinct from the nitrogenase. To improve the hydrogen production, different buffers, temperatures, pH values and some inorganic cofactors were studied. The results revealed that the best buffer was Tricine-KCl, the optimum temperature was 25 degrees C, the optimum pH value was within the range 7-7.5 and the optimum concentration of nickel chloride was 50 mu M that improved also the growth of O. chalybea. The influence of inorganic cofactors showed that the addition of 10(-5) MnCl2 increases the photoevolution of molecular hydrogen. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.