Rhodopseudomonas capsulata can use volatile fatty acids as electron donors for continuous H-2 production at the expense of light energy. In this study a mixture of acetate, propionate and butyrate was used as the substrate for continuous H-2 production from a photo-bioreactor seeded with R. capsulata. For a mixture of acetate 1.8 g/l, propionate of 0.2 g/l and butyrate of 1.0 g/l, a maximum H-2 production rate of 37.8 ml/g dry weight (dwt)/h, a light conversion efficiency of 3.69% and a substrate conversion efficiency of 45% were achieved. Hydrogen was also produced with the effluent from an acidogenic H-2-producing reactor at a maximum production rate of 24.9 ml/gdwt/h by R. capsulata. The H-2 yield increased by three-fold through combining H-2 production of anaerobic fermentative bacteria and R. capsulata, compared with the dark fermentation only. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.