The efficiency of hydrogen production by different cyanobacterial species depends on several external factors. We report here the factors enhancing hydrogen production by filamentous non-heterocystous cyanobacterium Arthrospira sp. PCC 8005. Cells adapted to dark-anaerobic conditions produced hydrogen consistent with increased hydrogenase activity when supplemented with Fe2+. Stimulation of hydrogen production could be achieved by addition of reductants, either dithiothreitol or beta-mercaptoethanol with higher production observed with the latter. Additionally, Fe2+ and p-mercaptoethanol added to nitrogen- and sulphur-deprived cells significantly stimulated H-2 production with maximal value of 5.91 +/- 0.14 mu mol H-2 mg Chla(-1) h(-1). Glucose and a small increase of osmolality imposed by either NaCl or sorbitol enhanced hydrogen production. High rates of hydrogen production were obtained in cells adapted in nitrogen-deprived medium with neutral and alkaline external pH, significant decrease of hydrogen production occurred under acidic external pH. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.