the research described presents a method for chemically modifying the surface of green plant photosynthetic membranes in such a way that electrical contact can be made. colloidal platinum was prepared, precipitated directly onto photosynthetic thylakoid membranes from aqueous solution, and entrapped on fiberglass filter paper. this composition of matter was capable of sustained simultaneous photoevolution of hydrogen and oxygen when irradiated at any wavelength in the chlorophyll absorption spectrum. experimental data support the interpretation that part of the platinum metal catalyst is precipitated adjacent to the photosystem-i reduction site of photosynthesis and that electron transfer occurs across the interface between photosystem-i and the catalyst. when contacted with metal electrodes, the thylakoid-platinum combination is capable of generating a sustained flow of current through an external load resistor. procedures for preparing this material and experimental data on its catalytic and electronic properties are presented. 14 refs., 6 figs. (era citation 13:046489)