1. A subcellular system derived entirely from the photosynthetic green sulfur bacterium, Chlorobium thiosulfatophilum, reduced NAD+ and NADP+ in light-dependent reactions. 2. The rate of NAD+ reduction was twice that of NADP+. 3. The reduction of NAD(P)+ required chlorophyll-containing particles, ferredoxin, and a soluble protein fraction, which catalyzed a reduction of NAD(P)+ with reduced ferredoxin. The soluble protein fraction could be replaced by purified ferredoxin-NADP reductase from spinach chloroplasts. The chlorophyll-containing particles photoreduced ferredoxin with sodium sulfide or 2-mercaptoethanol as the electron donor. 4. The rate of NAD+ reduction was comparable to the over-all rate of CO2 assimilation by C. thiosulfatophilum cells. © 1969.