Abstract: Spinach chloroplasts treated by incubation with Naja naja venom, or with phospho- lipase A purified from it, lost their activity in the reduction of NADP, ferricyanide, MV, and DCPIP and the concomitant evolution of O2. But if benzoquinone or thymoquinone was added as electron acceptor, O2-evolving capacity of such chloroplasts could still be shown. On the other hand, when DCPIPH2 or TMPDH2 was added as electron donor, NADP- or MV-reducing activity could be demonstrated. These results suggest that the site of inhibition of the Hill reaction by venom is located between Photosystem Ⅰand Photosystem Ⅱ. Plastoquinone is probably the point of disjunction of the electron transport chain. The incubated chloroplasts were examined under electron microscope. It was found that the lamellar membranes of grana were swollen up and disintegrated to varying extents depending on the duration of incubation.