Chloroplast membranes contain firmly bound nucleotides. Their synthesis seems not to be dependent on energy. The amount of labelled firmly bound ATP extracted from membranes after incubation in the light of the presence of 32Pi is only slightly affected by uncouplers such as desapidin and CCCP or energy transfer inhibitors as phlorizin at concentrations where steady state phosphorylation is completely abolished. With Dio-9 or NEM, however, the labelling of firmly bound ATP is lowered to a similar extent as the steady state phosphorylation. These effects can be explained assuming a direct modification of the coupling factor. The results of a two stage incubation experiment using a rapid filtration technique support our earlier hypothesis that the gammaP in the liberated ATP does not origin from the previously built phosphorylated intermediate.