In order to construct a molecular device for photoinduced hydrogen production, a model has been designed and first results in the framework of this multicomponent system are presented. This device should involve Photosystem 1, Photosystem 2 and hydrogenase in a modular configuration which allows to combine appropriate proteins from various-mainly thermophilic-organisms. Parts of this modular system can be easily exchanged and separately characterized and optimized. Here the optimization of one component of this device, the hydrogenase from Thiocapsa roseopersicina, is shown. The isolated hydrogenase was deposited as Langmuir-Blodgett (LB) film on quartz glass and ITO electrodes, respectively, and its activity was measured in dependence of counter ions, presence of oxygen and number of immobilized layers. While poly-L-lysine or poly-butyl-viologen as counter ion in the subphase stabilized the protein complex on quartz glass (up to about 30 mN/m surface pressure), Ca2+ resulted in a dramatic activity loss at a much lower surface pressure (15 mN/m). Also, the presence of even smallest amounts of oxygen or an excess amount of protein on an ITO electrode resulted in a significant decrease of the hydrogen production as did the increase in the number of layers-as shown by electrochemical measurements. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.