Treatment with NaHSO3 induces a 10-fold increase in H-2 photoproduction in the filamentous N-2-fixing cyanobacterium Anabaena sp. strain PCC 7120. However, it is unclear whether this treatment also increases H-2 photoproduction in green alga. In this study, treatment with 13 mM NaHSO3 resulted in about a 200-fold increase in H-2 production in Chlamydomonas reinhardtii, and this increase was most probably the result of reduced O-2 content and enhanced hydrogenase activity. Compared to the conventional strategy of sulfur deprivation. NaHSO3 treatment results in a higher maximum rate of H-2 photoproduction, greater efficiency of conversion of light energy into H-2, shorter half-time to produce the maximum accumulated H-2 levels, and reduced costs because no centrifugation is involved. We therefore conclude that NaHSO3 treatment is an efficient, rapid, and economic strategy for improving photobiological H-2 production in the green alga C. reinhardtii. (C) 2011 Elsevier Ltd. All rights reserved.