Photoinduced hydrogen evolution was investigated by use of a zinc porphyrin, EDTA, viologens and hydrogenase (H(2)ase) in the solutions and Langmuir-Blodgett (LB) films. An almost linear increase of hydrogen evolution rate was observed with the increase of H(2)ase concentrations from 1 to 5 mug/ml. For the zinc porphyrin, EDTA and methyl viologen, when their concentrations increased to a given value, hydrogen evolution did not show obvious increase. Phospholipid-porphyrin mixed LB films were prepared and used as photosensitizer for the photoinduced hydrogen evolution. Spectroscopic studies of the deoxygenated solutions indicated a "new" absorption band (in the solutions) or sharp peaks (in the LB films) when the sample solutions were irradiated, which was ascribed to the formation of an excited complex of porphyrin-EDTA (or -EDTA breakdown products). This excited complex was unstable to air. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.