We report on a biophotocathode based on photosystem 1 (PS1)-Pt nanoparticle complexes integrated in a redox hydrogel for photoelectrocatalytic H-2 evolution at low overpotential. A poly(vinyl)imidazole Os(bispyridine)(2)Cl polymer serves as conducting matrix to shuttle the electrons from the electrode to the PS1-Pt complexes embedded within the hydrogel. Light induced charge separation at the PS1-Pt complexes results in the generation of photocurrents (4.8 +/- 0.4 mu A cm(-2)) when the biophotocathodes are exposed to anaerobic buffer solutions. Under these redox hydrogel conditions, the protons are the sole possible electron acceptors, suggesting that the photocurrent generation is associated with H-2 evolution. Direct evidence for the latter process is provided by monitoring the H-2 production with a Pt microelectrode in scanning electrochemical microscopy configuration over the redox hydrogel film containing the PS1-Pt complexes under illumination.